Skilljam seems to be the 500 pound gorilla although I came across gamerabbit recently which seems to be pretty big as well. Skill gaming is definately here to stay.
The only thing that bothers me is that it originated from the spam network that spawned myspace. Gives me a funny feeling about what the tracking may be like. Generally I would like to see a revenue share option with skill gaming programs but gamingpartners only offers you a sad $10 CPA which is slightly discouraging.