This should be included in every FAQ :)

I can answer from my expirience:
- 1 have tried trafffic exchangers - they give nothing - people just visit your site like 1000 other sites in 1 day, so chance getting refs is small
- paid mails - better, but mostly there are low results, you need to be lucky
- ads on buxes - better than paid mails and traffix exchangers, but it is also the most expensive option
- and the last one is my favourite: - site like that, they are cheap - from $2/Year, and gives preety good result.

Advertise Your Reflink! - is preety good as i already said, PageRank:3 - the same as this forum, so you can imagine how popular it is, and it is not expensive - prices starts from $2/Year for 20x20 pixel ad - not so bad :)