I'm using Google Ads and
Clicksor...and also
Allfeeds.com to replace the public service ads on Google...Clicksor is ok....and they also have contextual ad links which I find pretty useful on forums....
I've created a simple tutorial on how to integrate it into IPB, you can check it out
here...
...and Clicksor pays in Paypal...which I find pretty useful
Hope that helps =)