here are all the dps dot specs on imp side:
lethality-operative
hatred-assassin
virulence-sniper
innovative ordnance-mercenary
madness-sorcerer
pyrotech-powertech
vengeance-juggernaut
annihilation-marauder
pyrotech has very strong aoe attacks with its flamethrowers and dots
IO has the highest damage in game right now,but I would count on this being nerfed down to normal soon.
Hatred has good aoe and lots of selfheals this would be very good for soloing stuff imo.
madness also has good selfheals but is doing very low damage this spec might be buffed soon.
annihilation has small self heals I find this spec kinda boring but it does pretty good damage.
vengeance has pretty good defensive skills and one of the best animations in the game imo.
virulence this is the spec I know the least about so I will leave this out.
lethality is a midrange spec with long ramp up times its pretty interesting and quite unique among specs.
good luck