Free Net Pass is my favorite right now. I use all of the AVS's to varying degrees, but FNP has the most webmaster friendly rules. They also have free hosting for their sites, have a good selection of free content to use, and have an active linklist to get some traffic back from.
For premium type sites I like
ProAdult Quantum , they have great rebills and very good link list traffic. They have freehosting available, but I think you get paid less per sale if you use it.