If you read on the many threads here in DP you will definitely find a whole lot of information about your question. But anyways, you can try Adbrite, Bidvertiser, and YPN if you live in the US Thanks JulieV
I think the best alternative to adsense is putting banners on your site for clickbank products that are related to your niche and that pay 75%. If you promote a product that pays $50, and you sell one every 100 clicks, then you are getting $.50 cents per click. That's a lot better than what adsense usually pays, and if you pick a quality product that is related to your niche topic you will most likely have a high conversion rate, I've had anywhere from 1 sale per 30 clicks to 1 sale per 200 click depending on the niche and product.
try to make your own products and sell it in your website (something different) or if you have high pr sell the banner / ads space.
Here is a list of adsense alternatives, you may find a good ad network in this list: forums.digitalpoint.com/showthread.php?t=816484
Chitika Premium is one the best alternatives IMO. Widget Bucks is good for products site. You can find an exhaustive list here
there are no other 'good' alternative to adsense in terms of revenue but similar alternatives would be chitika adbrite bidvertiser, etc.