I've got no experience in shopping around for ads, was hoping you did :) My blog gets decent traffic these days, seems like I should stick an ad or two someplace so it pays for itsself.
I initially started with Google Adsense, but has later moved to Freestar. They basically connect you with 10+ ad networks (including Google Adsense) and then all the networks will compete for your ad space each time an ad is shown. In my experience the revenue is a lot better.