I used to play eve which I really enjoyed but found I no longer had the time to make a real impact on my playing.
Also playing WoW as well but might need a break - couple of my mates are going into star trek when it launches for a break but not sure myself.
And have played (in no order):
Warhammer - stopped as my old PC couldn't handle it
D&D - was ok might reinstall now it's free to play
Guild Wars - not too bad but none of my mates played it

SWG - all I'll say is it was SOE's fault

CoV/CoH - good fun but groups were difficult to get at times
I might also give LOTRO a go since it has a free trial