Where is the SpamAssassin or DNSBL for Web Spam?

A lot of us thing that web spam is Google's problem, but many of us build systems that process untrusted URLs (for instance, social media sites, content aggregators, directories, etc.) There are services that are are aimed at blocking comment spam, but I'd really like something that, given a URL, tells me if the site is a "blight" site: for instance, not associated with Clickbank, Acai berries, stuff like that.

Does anything like this exist?