Widgetbucks.com is a young program which seems to be a good alternative to Adsense. People are still very skeptical about this program, because it seems too good to be true. Some people already had some problems with their accounts being blocked or closed for invalid clicks or for abuses, but such things happen with adsense too.
I have tested Widgetbucks and they are doing pretty good compared to other programs but they were not doing better than adsense for me. Anyway, it all depends on your site niche I guess.
Here are some opinions about Widgetbucks I got so far:
1) their ads may look catchy for some people
2) they have good CPC
3) easy to signup, easy to install
4) they pay by both check and paypal
1) they are new and probably unexperienced in some aspects
2) you have to wait 45 days to get a payment
3) the ads are in flash and they are slow when loading
4) some people complain about blocked accounts
Anyway, you should try Widgetbucks yourself and see how it performs.