It depends on the niche. For me my next best earner is ebay...but some sites aren't always good for ebay products!
If u has many US, UK visitor, chitika & clicksor will be the choice after adsense if not then choose bidvertiser, adbrite
If you are from States, then you surely have the option of YPN which not many people here have... Other than that....I would suggest bidvertiser. Regards, RightMan
I have heard mixed feelings... I have actually heard Adsense "skims" off the top... Not being a HUGE earner on adsense nor any other PPC I have no idea... My buddy swears up and down, he had adsense on his site, got about 1-2 clicks a day (if that)... He then switched to adbrite and he states he is getting 50+ clicks a day... He is my friend in real life, and I have seen his stats, so who knows...
Hmmmm... I use HotWords ( http://www.hotwords.com.br ), it's a "in-text" ads service, similar to Text Link Ads. I earn less with it than Adsense, but at least there is less burocracy to receive.
At least Kontera offer useful technology in PPC advertising. The contentlink flex ads are a good idea and i'm sure they can pay well if you pick decent niches. As far as traffic goes, I am not experienced in the programs, but I would imagine that all off Google's rivals pay pretty low - with Adsense not exactly offering amazing payouts at the moment either. I know it's not easy, but going direct with the merchant and working as an affiliate is always the best way to go. Problem is always the task of converting sales which is never an easy thing to do.
I am amazed that no one is measuring one against the other directly. Place adsense on your site for 1 month...then adbrite for 1 month etc. Even if the traffic changes you will still be able to compare CTR and ad revenue. Every one posting above has an opinion but let's hear some facts from a controlled study. Factor in that all ad network payout vary depending on their stock levels...that's why one month is the minimum time to test....and don't change anything else on your url