Theres probably alot of them, these are the ones I've actually gone and tried and tested repeatedly.
Sableye-
Don't laugh, it can easily shut down most physical pokemon in the OU environment being able to Knock Off, Burn and Recover. Its sturdier than some people give due credit for thanks to a good recovery move and defensive typing.
Qwilfish-
As someone mentioned already, it already has Tentacruel's great typing. Its stats aren't terrible just nothing special and it has one of the most varied movepools available. Spikes, Destiny Bond, Explosion, offense are all available to the little guy. I often used it as my spiker since it could also provide a threat on top the only other being Froslass pretty much.
Hitmontop-
Much sturdier than anyone gives credit for with excellent special defense and high defense. Resistant to Stealth Rock with Rapid Spin, two great possible traits and a nice variety of powerful attacks. Also Intimidate variety is one of the best users of Bulk Up as either way you attack it, its not going to hurt much unless its STAB and super effective. The Technician variety can do some serious revenge killing with Technician'd Fake Out + 90 power Mach Punch.
Shiftry-
It learns Explosion, Swords Dance, Leaf Storm, even Leech Seed and Nasty Plot...nuff said.
Politoed/Wrath-
Really underrated. Poliwrath gets Hypnosis, Belly Drum, dual Fighting type, STAB Focus Punch, Water Absorb, Ice Punch (From Advance) and even Waterfall for STAB now and can still do some damage with Hydro Pump. Toed is similar except with less weakness, Haze/Perish Song and slightly bulkier and able to abuse Counter because of it.
Blastoise-
One of the most defensive Rapid Spinners around with Yawn, Haze/Roar, Mirror Coat and Counter.
Primeape-
95 base speed, Scope Lens/Razor Claw, Focus Energy, Cross Chop, Stone Edge = Higher critical than Absol with Super Luck. Gets U-Turn on top for quick escapes and immunity to sleep which always equates a easy switch.
Kangaskhan-
A complete powerhouse with great stats in everything and strong movepool, great trait which makes STAB Fake Out followed with Sucker Punch a pain to deal with, sorta similar to the second Hitmontop I mentioned.
Tauros-
This needs no introduction, Tauros hurts everything. Alot.
Lanturn-
Lanturn = Starmie rape. It laughs at even Grass Knot varieties which at best only get 60 power on it. The standard sweeper Starmie can do absolutely nothing to Lanturn.
Porygon2-
Its a pain to kill...it really is.
Ludicolo-
Not so much does well in OU as it does in 00bers. Ludicolo is one of the few things in the entire game that can stop a Kyogre rampage dead. Not even Blissey can wall Kyogre which gives you an idea how effective it is.
Miltank-
Physical Blissey. A really fast and strong physical Blissey.