Heres what i have tryed and there ok its real traffic not bots like most ppc website give you.
adknowledge, adsonar, pulse360, adbrite
and the scammers are EasySiteHits.com , bringvisitor.com , Revisitors.com , visitorboost.com , Clicksor.com
I'm sure theres more out there so do tons of reseaarch before doing business with PPC advertising businesses
Feel free to post whats working for you or what you know is a scam