The 7Search affiliate program is pretty good, they give you 50% of the the revenue generated from your traffic. You can set up search boxes and let your surfers pick the keywords or you can direct the traffic to specific keywords. They also give you a URL that lists the top bids at any given time, really handy for picking the top paying keywords. For a while last year I was getting $0.75/click on phrases like "buy viagra" & "penis enlargment".
The only negative is that their signup pages are cluttered and difficult to navigate, well worth the effort though.
I've been sending them exit traffic for over 2 years, they've paid me on time every month.
http://www.pay-per-search.com
http://www.7search.com