Pretty much every solo "amateur" site has a referral program and they have converted well for me. As far as sites offfering mostly images as their content solo girl sites are the best converters.
Here is the URL for the "friends" page on one of my sites. You can use this to surf different amateur sites and find the ones with referral programs.
http://www.allrealgirls.com/arp
A few things to watch for with these sites though.
1) Make sure they have content zips for you to use. It's nearly impossible to sell a solo girl site using stock content to promote it.
2) Make sure that they have a clean tour to run traffic through. Most of the "amateur" sites link like crazy to toplists & friends pages. They also pop sites like nastyfriends, findaslut, etc throughout their tour so be sure that you are going to send your referral traffic to a site that is free of leaks.
3) If a the program is a partnership program rather than pay-per signup get a pass for the members area and make sure that it is a decent site and that they are updating reguarly.
Hope this info helps you