Cor: Ice/Therm
Brute: SS/Dark
MM: Bots/FF or Nin/Dark
Stalker: EM/Nin
Dom: MC/Ice or MC/Nrg
Pretty much fotm, what I liked to play or what I havnt liked to fight too much.
Stalker:
You want either nrg / nrg or spines / sr. Most likely nrg / nrg cause then you can have a solution for bubbles without having a kin on the team.
MM I would prolly go merc / ff, those web granades are darn usefull. But it seems like bots are also good.
For brutes its nrg /*. Nrg primary is superior to ss in many ways. The secondary is very very hard to choose but I have a strange feeling nrg is good.
For Dom, I would suspect a fire / fire dom. Smoke is darn usefull with a team that relys on its team being invisable and the damage seems to be best from */fire. If this doesnt work its ice / nrg for the slows or mind / nrg for TK.
Well right now this would be my solution, I will know much more when I have actually played a couple of villains to lvl 40 or hopefully soon 50.
50s
controllers: Ill rad , grav rad, fire kin, ice kin
blaster: ice em
scrapper: spines sr
Hmm, didnt think of fire for smoke, went for EM/Nin though for its -perc power.
While EM for dam type is much better for brute I found rage was easier to build with SS and in longer fights this could be useful as unlike PvE you are probably going to gain fury through outgoing attacks then incoming.
Personally like MC/Ice. MC for TK and ice for greater protection and power boost and slows (really depends if your fighting heroes or villains but */Ice cannot be ASed).
Therm for forge mainly.
Nin MM probably does the most damage and has alot of stuns and trops. Again depends what your up against imo, Bots have -regen on their attacks so could be used to help take down regen scrappers.
Sorry to put this in 2nd post, just thought I would explain my choices.
Corruptor: */Thermal - great buffs and one awesome debuff (Heat Exhaustion), with my pick of primaries being either Ice (slows and ST damage), Sonic (-Res and mezzes), or Rad (low endurance, -Def, ST disorient).
Brute: EM/Fire - The penalty of poor shielding is negated by the shields from the Corruptor - what's left is a highly mobile, offensive Brute with the best burst damage capability (Fiery Embrace + Build Up) and a readily-available self Heal (Healing Flames), with the gaps in healing being filled in by the Corruptor. Low-cost shields in addition to a good self +End in Consume mean that /Fire is more self-sufficient than most secondaries as well. EM provides disorients on top of high damage - this isn't a major concern, but it's always good to have something that can throw the opposition off their stride.
MM: Robotics/Dark - -Regen in ranged attacks, with the inherent weakness being negated by the shield in the secondary puts Robotics over Mercs for me; Dark is full of too many tricks to ignore, with Tar Patch, Darkest Night, Fearsome Stare, Howling Twilight (as debuff), Dark Servant all being more preferable in my eyes than, uh... bubbles. 
Also, Twilight Grasp seems like it will work fantastically well with the new Bodyguard system - I've always been a fan of proactive defence, especially when you can stack -Acc in the process. 
Stalker: EM-or-Spines/EA - EM for high damage, Spines to be annoying as all hell, EA for the reasons Imaginary listed. (I'd expect other members of the team to have Grant Invis as well.) The build would ideally be a more Assassin-esque build than a Scrappery build, but it'd be down to the individual concerned as to how they play it.
Dominator: Plant-or-Mind/Thorns-or-Ice - Maybe my view is skewed by playing alongside Filth's Dominator, but Plant/Thorns can turn an opposition force inside out. Mind is undeniably good, and shouldn't be ignored; /Ice might seem an odd choice, but the fact that Doms get a +modifier to control effects means that the slows would be cripplingly effective.
YMMV, of course. 
@Synaesthetix
"Here, take some more bees with you. You may need them."
Union: FU//LoUD
"that Syn is that that" - Mothers Love
imaginary u didnt post a corruptor
i think its the hardest choice with the front runners being sonic, thermal or kin, all have gr8 buffs and debuffs
Brute - Nrg/Invun
Corrupter - Ice/Thermal
Dominator - Plant/Nrg
Mastermind - Ninja/FF
Stalker - Nrg/Ninjitsu
The brute will act like my Invun/Nrg tank, but will do more damage, how ever he wont be able to take as much damage.
Corrupter, he will act like a healer, with fort(Forge), res to energy damage (pfft what */nrg blaster?), -Regen for regen scrappers and a -res power.
Dominator, Plants has Slows, holds and imobs. Also does ALOT of single target damage, acts like a ice/nrg blaster .
Mastermind, Ninjas, has alot of slows, in the form of caltrops, and does decent damage. Takes a while to setup though. :s FF for the defence
Stalker, Biggest Single target damage out of the sets. Ninjitsu is like an improved SR with a self heal. Good controller killer.
It's a tricky one, with the right team I've come up with a combination that would simply own:
Brute: Dark Melee/Stone Armour - DM is awesome in PvE, awesome in PvP 'nuff said, the heroes will 'fear you' :P. Stone - the roughest, toughest there is - what can hurt a mountain? nothing. What can a mountain hurt? nothing. What can move a mountain? nothing. says it all.
Corruptor: Assault Rifle/Traps - ever seen what FULL AUTO does to a Granite Tank? That you should see, what Full Auto does to a Granite Tank you should see; the thing shreds heroes. Traps - one word: Time Bomb. What is good in PvE becomes awesome in PvP, Traps is worth it for this one power.
Dominator: Gravity/Psionic - damage all the way. Your team manages to corner a difficult controller? slap on Dimension Shift - "game over dude" a good one for high damage teams. Psionic - Drain Psyche - fighting a Granite Tank again? if they've got no Endurance, they've got no toggles, it's like an 'I win' button for villains.
Mastermind: Necromancy/Traps - 'you cannot kill what does not truly live' good one if you like to stay at range. Traps - two words: Force Field Generator - possibly the best Mezz buff for villains in the game, especially if you have superspeed as a travel power.
Stalker: Ninja Blade/Regen - Ninja Blade was probably optimised for PvP and if you play with a Ninja Mastermind you can disguise yourself as a henchman - deception is your cheapest toggle :P. Regen - yes it's overpowered, yes you'll get complaints for using it from Heroes, but there's a reason it rules in PvP: head and shoulders above the other secondaries.
what wud ur ideal villain pentad team be? think the hardest choice is the corruptor, will b interestin to see what people think