AdBrite has been termed as the best alternative to AdSense. They provide reasonably large selection of ad formats. Clicksor is another good option especially for small and medium publishers. But the best of them all thats worked atleast for me is Infolinks... Some other Adsense Alternatives worth trying are http://adsensealternativesblog.com/
anything to back up those statements? I've never used anything other than adsense, but my assumption would be that its the best considering the amount of people bidding on ads.
Clciksor has high CPM rates, but they show low impressions a day for your website . Adbrite shows correct impressions you get a day . I receive 50K impressions in adbrite and 10K in clicksor. Even though clicksor pays more CPM .Its a scam .