Overture (formerly Goto). Since they have partnered with yahoo, msn etc. the traffic they send me has doubled in two months. So I can recommend them if you want more traffic.
I'm glad that most of my listings are still 1 and 2 cents (old goto-style), but nowadays you'll have to bid at least 5 cents to get listed. In my opinion only worth a try, decide afterwards if it was worth it.
Advertising income is still larger than hosting & overture, but I'm hoping for better times
[ But don't count the hours I spend & spent on it ]