I have been an affiliate of DirectNIC for a couple of years. In 2004 I created a site from an expired domain name that I bought and started adding expired doman names to it everyday just like Nameslot suggested.
The database now has about 19 million expired domains. I have been earning some comission from DirectNIC, despite the fact that they charge $15 a year (I get $0.50 per sale ). It works out to about $30 a year (I can buy two domains there...). I tried another one, Registerfly, but that didn't work well and then I heard they had problems, so I went back to DirectNIC.
Last year I looked into becoming a reseller and almost went with Godaddy's program, but it cost $100 and I didn't like having to pay to make them money...! Other reseller programs make you pay money upfront into an account and then buy domains from that, more than I care to tie up.
So I'm also looking for a good affiliate program or reseller program.