1. Articuno is a beast; I used one in OU because I had ice for the monotype tourney in round 1. It takes a STAB fire blast from heatran and roosts it off like a champ. It's hella hard to take down, but it's just offputting because of it's horrendous typing and awful 4x SR weakness.
Glad to see Articuno getting shoutouts from people who aren't me :P. Just keep in mind that if you're using it as a Milotic counter that you still need some way to deal with RestTalk, unless you're using enough non-damaging attacks to sit there and stall it out of PP with Pressure. It is a great asset to have against Bulky waters, especially if you're running a Grass-type that can't afford to take an Ice Beam. The biggest problem is that Steel-types shit all over it, setting up Stealth Rock, resisting Ice, and being immune to Toxic. Still, it can be beastly with support, since while some things totally beat it, it has a pretty high number of UU pokes that it can take on while barely losing any health. Thus, if you scout the enemy and take out the right pokemon, Arti can sometimes destroy half the opponents team. I've used it to great effect on my main team. It's definitely fun to see the defensive set finish off a weakened Moltres after eating a Fire Blast :) (I don't recommend this unless it's desperate though). Unfortunately, if you don't keep Stealth Rock off of the field, Articuno's switch-ins are pretty much limited to bulky Waters and Grassers.
2. I've never used Raichu, but I remember when I first started UU, I used a SubManectric and it beat a lot of things. Electric is a nice offensive type, but I always feel like I'm being redundant when I use it alongside a grass-type. I just lean towards grass because it has better defensive typing.
3. Offensive Milotic is so overrated. It's pretty much dead weight against stall and can't really counter the things it's "supposed to". I guess because it's offensive, it shouldn't, but there's just better options imo.
Try the Life Orb tank set. It has more power (since it's Modest) and has just enough bulk to survive the moves it needs to and retaliate. It doesn't hard counter things all day like the bulky set, but it's a good mix of power and bulk. This comes at the cost of speed, however.
Also regarding Franky's shoutout for Tauros: I'm actually baffled why Tauros doesn't see more UU use. 110 Speed + 100 Attack is damn good considering Tauros' STAB and coverage moves have 100 BP. If you're running Life Orb, Pursuit is an option to deal with Ghosts in certain situations. It's great insurance against Mismagius. Attack as it sets up, switch Tauros in on Shadow Ball, then kill it with Pursuit (~50-60% iirc) or Stone Edge (~80%).
@dbcb
The two main spreads are:
for support - 252 HP, 252 SpDef, 4 Spe. This is the one that survives Moltres' Fire Blast, takes 40% from Specs Zam Psychic, and counters Rotom and Lanturn despite the type disadvantage.
or the SubRoost - 252 HP, enough speed to beat Milotic (I think its 216) and the rest is useful in literally anything else, except attack. I prefer Defense. This one is still very bulky, but it's no wall. The speed and the bulk together make a dangerous combo, though. Only use this if you have Registeel firmly covered, and don't have waters well covered, though. Otherwise Moltres is superior.