Chitika, the leader is products related ads now released their content based ads for content sites. According to their latest newsletter (published on 12th May, 2008), they will also be serving content ads like Travel, Vacation, Entertainment, Mesothelioma, Finance, Sports etc.
The ads are delivered as CPC, CPA and CPM based to ensure high earnings for publishers. Well, with all this, Chitika gonna be the best alternative to Google Adsense in my opinion.

The ads will be served as Premium ads, thus making it available only to US visitors as they are behaviorally targeted in nature.
You can find more information about Content Ads and Chitika Premium Ads on their official blog.