If so, which one? Is Adpeeps worth it?
Do you mean an ad rotator? I use a really simple one through wordpress called adrotator! (ironically) and it rotates my banners. Is that what you're looking for?
I just have some manually-coded 125x125 ad blocks on my WordPress-powered blog. The five ad blocks are static, instead of rotating, and therefore, are theoretically worth more. On another site, though, I have a bare-bones PHP rotator that works pretty good. (It just picks a random number and shows the banner assigned to that number.)
I use Adserve on a WP site to show up to 5 125x125 box ads with the addition of a little extra PHP to rotate the order of the ads in their section randomly.
I like Adserve because it's easy for clients to add and remove the box ads by themeselves plus it keeps a record of how many times the ad is clicked.