www.valueclick.com <--- very good the best but picky on whom they approve into their network www.rydium.com <--- not as picky but j ust tends to allow tech related sites into their network. likes to throw spyware ads in and denies that they do. Also on two seperate ocassions one of their advertiers included an IE exploit in their flash ad. However they removed it.
ValueClick pays every other month Rydium every 3 months.
Valueclick pays more per click then rydium but rydium pays more per CPM then Valueclick does.
to bad I can't give you my refferal link through here. I wouldn't mind making 10% of what you make for the next year lol.