www.revenuegateway.com - should be known to you, since a GFY'er is very much involved in running that program. Only problem I have with that program is that the the companies that use it, come and go. So you HAVE to use a Bannersystem when placing your banners on your site. Because you WILL need to replace them at some point, and you dont want to do that by hand.
www.regnow.com
You can sell almost every kind of software from them. The old regnow had problems tracking the sales, but the new script works. But if you use them, remember to check your stats once in a while
There are more programs out there, but these hit a wide segmant of surfers, and I use them myself.