from my own experience i know its very difficult to whore poker sites to build a roll. imo it better to grind out 500 playing 10nl and start whoring with 25nl. it´s not only annoying to clear a bonus at the speed of a snail, but at most sites that offer x% bonus you´ll miss cash depositing $200 or so.

DreamPoker offers 25% up to $50, to clear at 5 raked hands/$ with a rh defined as rake >=.25

at rooms where rakeback is unavailable you might combine your whoring tour with signing up through one of the webs large affiliates. some of them offer additional cash bonuses.