Adult friend finder is one of the most popular affiliate programs for adult webmasters. They also have a slew of other sites to promote. If you want to promote cams.com, or Penthouse.com, or ALt.com you need to sign up for this affiliate program.
Plenty of good banners. Not a lot of galleries for the penthouse web site, but overall great promotional tools, and several options for getting paid based upon traffic or signups or rev share.
They also are the program for bondage.com, Danni.com, getiton.com, lesbian personals, and several others.