Depending on your site, there are several. Many ask for you to already have hits in the thousands, others accept you, no questions asked. Here are a few that work for me.
- Chitika -- Places packets of links on your site and other options.
- InfoLinks -- One of the best, with various options as to how and when something is places. Includes very attractive floating banners that are real eye-catchers.
- Earnify -- Very recomended, but picky. Unless your site already has good traffic they won't approve the site.