Blaster: Rad/Mental - He can fight strictly ranged or blapper style, or a little of both. The best blaster makes you pay for trying to run in and melee you.
Defender: Rad/Water - The best Soloing Defender I have ever played, better than Rad/Rad because Water attacks are faster.
Controller: Illusion/TA - PA plus Oil Slick Arrow while Superior Invis'd is very safe.
Scrapper: DA/Katana - I don't play scrappers much, this is my old school toon.
Tanker: Fire/Savage or Rad/WM - I farm with tanks. Fire/Savage handles +4/8 easily vs Fire. Rad/WM vs Energy or SL.
Brute: EM/Inv - I don't farm with Brutes. This EM builds fury fast enough and Inv has its weaknesses, you just need to know the games foes to play this Brute best.
Corruptor: Energy/Traps - Set up the Bombs and Fold Space, then Energy blast the minutiae into the walls.
Dominator: Darkness/Martial - I don't play Dominators much. This is the Combo I took to 50 and incarnated.
Mastermind: Bots/Elec or Thugs/Emp - I play MM all the time, can't pick a favorite from these two, sorry.
Stalker: SJ/IceArmor - Play it like a Traditional Stalker with Chilling Embrace turned off. Play a team-based style by using CE, Icy Bastion, and Energy Absorption and all your great SJ moves.
Sentinel: BeamRifle/Ninja - A hover blaster who never gets hit, and never needs blues or greens. Feed him big reds.