I also highly reccommend poker.com. They are really easy to get in contact with (most are on MSN at all hours), they have a great affiliate interface with tons of goodies, not to mention they have great promotions for their affiliates. I won 1 of the prizes in their last contest which was a trip to the CAC in vegas package worth $2000!!! I am about to leave in an hour 😎 One of the great features is if a player clicks on one of your links, but doesn’t sign up, if they go back to poker.com in I believe 1 year, you will still receive credit for the sign-up.
If you aren’t promoting them yet, I would suggest you do!