Raticate: Dark, U-Turn, Electric, Psychic, and weakly Fire and Fighting. It's also got way too many Special moves it shouldn't be using. Dark/Electric? Sucker Punch can let it overcome its 97 Speed against the truly fast.
Kangaskhan: Dark, Outrage, Ground, Fighting, Ghost, Fire, Electric, Ice, Water, and I guess Iron Tail. Dark/Ghost, Dark/Ground, Ghost/Ground, Water/Fighting, Water/Electric.... there's plenty of good options to choose from. Mega kangaskhan isn't legal, but regular Kangaskhan might be worth a look-see anyway.
Tauros: Psychic, Ground, Rock, Electric, Steel, and Outrage. (It's also got some Dark options, but it's stuff like Payback) Sheer Force Tauros running Psychic/Steel could be worth a look-see. If you're running STAB Earthquake, Sheer Force is less appealing, being irrelevant to Earthquake, so probably stick with Intimidate if going that route.
Persian: Dark, Fairy, Rock, Electric, Ghost, Flying, U-Turn, Poison, Grass, and Foul Play. It can pull off both Physical and Special with similar competency, and with Technician it can do stuff like run Thief over Crunch and run Flying at all. (Aerial Ace) Worth a shot? Keep in mind some of its options are exclusively Special (Power Gem for Rock) and others exclusively Physical. (Play Rough for Fairy)
Lickilicky: Only slightly better at Physical than Special, actually, and it has Cloud Nine, so if weather teams become a big deal it might be worth considering for that alone. It can run Physical Grass, Steel, Dark, Ground, Fighting, Dragon Tail, Psychic, Water, Fire, Electric, Ice, and Iron Tail. (Also, Explosion) On the Special front it can run Ice, Fire, Electric, Solar Beam, Ghost, Fighting, and Water. Worth noting that it gets Curse and Belly Drum -overall it's probably better off sticking to the physical end of things just because of those. It's too bad it doesn't get Drain Punch or anything, though. Nor priority. Very flexible and fairly strong, anyway.
Blissey: Realistically speaking, you're probably making Eviolite Chansey and slapping on a defensible typing. But if you do want to run a Blissey that can attack, its options are Ice, Fire, Electric, Ghost, Psychic, and Fairy.
Ditto: Just give it a double resistance to Stealth Rock or make it Flying/Ground or Rock or Fighting (Stealth Rock+Spikes and Toxic Spikes protection) and call it a day.
Snorlax: Dark, Ground, Fighting, Rock, Electric, (Why does Snorlax get Wild Charge??) Psychic, Self-Destruct, Ice, Fire, Electric, Steel, Poison, Grass, and Outrage. Also keep in mind it of course gets Curse. If you're going to make it part-Steel (Or Poison) remember to not give it Immunity, stick to Thick Fat.
Porygon-Z (Or 2): Already the subject of much discussion, but nonetheless... Electric, Bug, Psychic, Ghost, Ice, Solar Beam, Dark, and Foul Play and Icy Wind are also worth noting. It's actually not that flexible, but even so.
Furret: Fighting, Ghost, U-Turn, Sucker Punch, Pursuit, Knock off, Fire, Ice, Electric, Water, and Iron Tail. Also a number of Special moves it's probably best off ignoring. Unfortunately, its stats are mediocre (90 Speed is nice, but not enough) and its best Ability is Frisk, so you're probably better off ignoring it in favor of some other Pokemon that can pull off its job better.
Ambipom: Flying (Technician Aerial Ace, plus it has Acrobatics), Fighting, Ghost, Dark (Technician Payback), U-Turn, Foul Play, Fire, Poison, Grass, Fury Cutter, Ice, Electric, Iron Tail and Knock Off. It also has Skill Link, though it has nearly no use for it. It also has an enormous Special movepool it has no business using. And of course it gets Baton Pass and moves like Nasty Plot, so you can potentially run it with a defensive typing and use it chiefly to benefit the team. It's very flexible.
Dunsparce: Ground, Ice, Ghost, Electric, Fire, Gyro Ball, Poison, Rock, Curse, Water, Psychic, and Iron Tail. Probably its best option is to focus on using Coil and its Physical options, though fortunately its only Ice and Ghost it of that previous list that it gets no Physical options for. Too bad it's slow and not that great. No priority, either.
Ursaring: Fighting, Ground, Ghost, Rock, Dark, Fairy, Fire, Ice, Electric, Poison, and Grass. It's really too bad Quick Feet is only a 50% boost to Speed. It's very flexible, but way too slow. Remember you can't use a Flame Orb to activate Guts if it's part Fire nor a Toxic Orb if it's part Poison or Steel. It has 130 Attack, so it might have a niche regardless of its crappy Speed. Too bad no priority.
Stantler: Psychic, Jump Kick, Electric, Ground, Ghost, Grass, Bug, Sucker Punch, Gravity, and Bounce if you care. Remember Gravity prevents Jump Kick from working. It's got the stats to run both Physical and Special, though not all its options are equally compatible there. (It's only Ghost option is Shadow Ball while its own Bug option is Megahorn) Mostly I'd give serious consideration to a Ground/Dark edition that uses Gravity, Earthquake, and Sucker Punch, maybe with Megahorn or Wild Charge for coverage.
Smeargle: Anything you want. Normally Smeargle wants a defensible typing, such as Flying/Steel or Dark/Poison.
Miltank: Psychic, Ground, Fighting, Steel, Curse, Fire, Ice, Rock, and Electric. It's actually fairly fast, tough, and hard hitting, and with Thick Fat and Sap Sipper can flexibly cover some weaknesses. Ground/Steel with Thick Fat seems one of its best options overall.
Linoone: Fairy, Ghost, Poison, and Grass. Also, Extreme Speed. Of these, Grass is the only one that doesn't cover Normal's weakness to Fighting, so Fairy, Ghost, and Poison could all be good to combine with its innate Normal typing. Extreme Speed is really its main claim to fame, so it probably should stay part Normal.
Vigoroth/Slaking: Fighting, Ground, Ghost, Rock, Dark, Fire, Ice, Electric, Poison, and Sucker Punch. Slaking doesn't seem to add anything in particular, unless you consider it worth going for its Special Attacking options.
Exploud: Fire, Ice, Electric, Ghost, Dark, Ground, Fighting, Water, Rock, and Outrage. Realistically speaking, if you're using Exploud it's for Boomburst, and honestly at that point you're probably better off going to Noivern. To be fair, Noivern doesn't get Scrappy.
Delcatty: oh man are its stats bad. Oh uh, it gets Fire, Ice, Electric, Ghost, Psychic, Sucker Punch, and I guess Iron Tail. Uuuh. Really, just don't use it.
Spinda: Sucker punch, Psychic, Ghost, Fighting, Rock, Electric, Fire, Ice, Electric.... but you know what I'd do? Put it on a V-Create Assist team with Contrary and a Choice Scarf, and make it Fire/type that compliments Fire. Otherwise, probably don't bother.
Zangoose: Fighting, Bug, Ghost, Dark, Poison (Don't do it though), Curse, Fire, Ice, and Electric. Fire/Fighting could be a good choice, or Fire/Dark. Fire just for the immunity to being Burned, which can really mess up Toxic Boost Zangoose builds. Or really, Zangoose in general.
Castform: There's an important question as to whether nicknames overrule the Form changes or are overruled by them. If Form changes win, then just go for hazard resistance and ignore this whole thing. If dictating type overrules Forecast's type changing, then it has Water, Fire, Ice, Electric, Ghost, Grass, Future Sight, and don't forget it can finally run Rock for Sandstorm Weather Ball STAB, which might even give it a real niche! (It is really hard to pull off a Special attacker that actually fits to a Sand team) On the other hand you can always use Rock Roserade or some such, so probably not.
Kecleon: Color Change and Protean make the question pretty irrelevant in regards to STABs. Instead you should focus on the considerations of hazards and what you need Kecleon to be able to switch on -in other words, if your team has a hard time switching in on Dark types, consider making Kecleon a Dark/Fighting, Fighting/Fairy, or Dark/Fairy type so that it's doubly resistant to Dark and will laugh off incoming Dark attacks when it's switching in.
Lopunny: Until Mega Lopunny comes along, it's not that notable, but even so... Fighting, Rototiller, Fire, Ice, Electric... er... Iron Tail?... Honestly, it's a bit narrowly focused in its movepool. It's too bad its stats don't really support a defensive style, because it actually gets Cosmic Power.
Bibarel: Curse, Superpower (Terrible with Simple), Iron Tail. Er. Don't bother.
Purugly: Ghost, U-Turn, Fairy, a number of Dark moves including Sucker Punch and Foul Play, and... Iron Tail?... I dunno, Dark/Fairy is about the only thing that stands out as particularly viable to me.
Regigigas: Fire, Ice, Electric, Fighting, Steel, Fighting, Dark, Ground, Rock, Psychic, and Gravity. I want Doubles Type Control so I can Entrainment Moxie onto a Ground/Fighting Regigigas and kill everything. Imagine a single tear running dramatically down my face at the thought this will probably never happen.
Watchog: Dark, Fighting, Poison, Water, Grass, Electric, Psychic, Fire, Ice, Iron Tail and a bunch of Special moves it probably shouldn't use. Mostly it's too slow, too fragile, and not hard enough hitting, with Abilities that range from OK to useless and no unique moves to help it stand out. Changing its typing isn't going to help when you can do that with everything else too.
Stoutland: Fire, Ice, Electric, Dark, Fairy, and Steel. Also kind of Fighting via Superpower and Reversal. I dunno, I wanna see Stoutland succeed but I cant help but suspect that there are plenty of Pokemon you could replace it with. On the plus side, it has Sand Rush, which only Excadrill and Sandslash share. (And Sandslash is Excadrill minus) So in a Sand team Stoutland could be your second Excadrill? To be fair, Excadrill doesn't learn Play Rough -a Fairy Sand whatsit has its good points. But outside of Sand I'm pretty sure Stoutland has too much competition.
Audino: Gosh, realistically just run a defensive typing. And save it for Doubles because Blissey/Eviolite Chansey is probably better in Singles. But if you wanna try to hit things with it... Electric, Psychic, Ice, Solar Beam, Ghost, Fire, Fairy, Water, Bug, Fighting, Knock Off and Iron Tail. It can run Physical or Special equally (poorly), but its movepool is much better filled out on the Special end of things.
Cinccino: Grass, Rock, U-Turn, Water, Knock Off, Poison, Iron Tail... Fighting (Technician Wake Up Slap)... honestly, if you're going to run Cinccino probably just go Grass/Rock with Skill Link, Rock Blast, and Bullet Seed. It's fast, hits fairly hard, Grass/Rock is two terrible types that taste great together, and even though the result competes with Mega Heracross it has notable advantages of A: being much faster and B: not being a Mega. Worst comes to worst, if your Mega slot is committed yet you find yourself wanting Skill Link Grass/Rock goodness, break out Cincinno. And maybe Band it, because otherwise you're nowhere near Mega Heracross' damage output.
Bouffalant: Bug, Ground, Rock, Poison, Electric, Steel, Psychic, Superpower, Outrage, and Payback. (It's slow enough going Dark for STAB might actually be worthwhile) Ground is appealing given that it has Sap Sipper, maybe run it as Ground Electric for good coverage?
Diggersby: Fighting, Rock, Electric, U-Turn. Fighting/Ground is a nice combination, and it gets Smack Down, so the likes of Skarmory can't just stick in on it indefinitely. Electric/Ground is also good, though utterly walled by Ground/Flying.
Furfrou: Sucker Punch, Electric, U-turn... uuuh... some Special moves... Wow. Um. Dark/Electric I guess.
Pidgeot: Heat Wave is about it for notable non-STAB moves. Ouch. Does not combine well with its unusual access to Hurricane. Probably just skip it, there's tons of Normal/Flying Pokemon to invalidate it.
Fearow: Ground, U-turn, Dark (sort of), er, Steel Wing... some Special moves it cannot support... urm. Ground/Flying is actually difficult to combine STABs for, but Empoleon can actually one-up it by using Earthquake instead of Drill Run. Blaziken can one-up it with Earthquake and Brave Bird! To be fair Fearow is much faster than Empoleon...
Farfetch'd: Hahahahahahahaha... oh, you're serious. Well, I guess it can run Poison, Dark, Grass, Curse, U-turn, Steel Wing... aaand that's it. Yaaaay.
Dodrio: Steel Wing and Knock Off are basically it. Hooray. Skip.
Noctowl: Psychic, of course, as well as Ghost, and Fire. Eeeeh. It does get Tinted Lens...
Swellow: U-Turn, Steel Wing... er... that's... really about it. Steel/Flying is overall a pretty straight improvement, anyway.
Staraptor: FIGHTING, Steel Wing, U-Turn, and that's it. Flying/Fighting is a pretty good type combination, so that's OK.
Chatot: Remember it gets Boomburst! Otherwise, Fire. Yep. Oh and there's Synchronoise, but why bother? (And if you wanted to use Synchronoise, the smart thing would be to make it Fighting/Poison) Mostly, if you want to use Chatot run Normal/Fire, basically.
Unfezant: Dark, Steel Wing, U-Turn. Yeeeeep.
Braviary: Superpower, U-Turn, Steel Wing, Ghost. Hooray for sucking!
Pyroar: Solar Beam, Dark, and a depressing number of Physical moves it lacks the stats to use that well. sigh
Heliolisk: Dark, Water (If you're not running Sun), Focus Blast, and a number of Physical moves it lacks the stats to use.
