I want to try and farm what I can without NEEDING others, but willing to add more when I can.
I'd go with a knight for your tank. Warriors are very gear dependent for aggro and tanking, but a knight will be able to hold aggro much easier. SK has snare, FD, and more DPS. Pally has a back up rez in case cleric dies, group heals, etc.
Cleric - best heals, rez, best buffs
Enchanter - crack, haste, mez - as powerful as bards are, the enchanter is going to be better + depending on your skill you can do a charm pet for a LOT of extra DPS
4th spot - DPS + utility - Options:
Druid - Snare, Ports, back up heals, DS, Dots, Nukes - lots of utility, but not the best at anything
Wiz - DPS, ports, snare
Mage - Pet, DS, mod rods, DPS
Necro - Pet, FD, Snare, Dots (not really great in group game atm), Rez (nice wipe saver)
Ranger - Autofire is very OP at the moment, rangers stay decent DPS, nice back up tank in a pinch, Weaponshield, snare
Zerker - DPS, Snare
That 4th slot is where you can get creative, but I'd stick with the trinity of Knight, Cleric, Enchanter. That 4th slot you can't really go wrong, but pick something that fits your play style too.