It is very clear that for websites with a wide range of subjects there is no program doing better than Google Adsense. And this is because they have a very much number of ads, some of them catchy even for experienced users and they also have pretty high CPC. However, some sites are not accepted by Adsense or some people get banned, so there is a big need for alternatives. YPN cannot be always considered because it only accepts US advertisers and it also requires some kind of invitation.
Here are some alternatives:
Kanoodle are serios and good , but again they accept very few websites.
Adbrite gives you a lot of freedom, but you don't make as much as you do with google, not even close.
If you don't mind having some naked little pictures on your site, you may try friendfinder.com programs.
Amazon and Microsoft also are trying to get into contextual advertising biz, but it is not known yet when.
The others such as clicksor, bidvertiser, etc are not worth trying.