http://dir.edgefishing.net/
Just a random domain purchase that had google traffic. It's not huge money, but if you diversify the links enough(be sure to let the SE traffic come in for a while to see what terms to target) the surfer will probably click something.
That domain only makes $10/day max, but I paid $20 for it and spent a few hours developing it. A worthwhile investment I'd say
Edit: The KW prices aren't very high for adult in most cases. For mainstream I'd say it's the way to go. You may want to look into sex.com's partner program for adult terms.