Currently I run: Google Adsense Value Click Burst Media Adbrite Clicksor For CPM, Burst Media is making me the most. CPM $2-$4 right now. Best CPC, Google Adsense so far. Worst for us has been Clicksor and Adbrite (literally pennies)
Try Adsdaq. They serve banners and stuff, but you get to set your own cpm price. They sell a portion of your inventory at this price and whatever is unsold goes to other ad networks of your choice. Here's my Adsdaq review.
I'm using Adsense... I've heard of some very low payments and earningsfrom adbright but haven't tried them!