Software to Run an Affiliate Program
I use and recommend Groundbreak's Ultimate Afilliate.
It is a CGI script written in Perl that sets up a full-featured affiliate program on your own web server - giving YOU total control. Instead of handing over your affiliate program to a third party, you can now run yours in-house without monthly escrow costs and per-transaction fees!
You can sign up as a "How to Add Games to Your Site" affiliate here.