I remember the site urlblacklist.com, it was a good resource for proxy owners, security managers, and application developers to test their idea before spending money on URL Classification services from a commercial vendor.
For some users this free solution was good enough to use even after the proof of concept, and for some users it was enough to secure funds/users and allow them to look for a commercial similar service, it was a win win.
Where did it go away? I read in a post a while ago that they forgot to renew their domain, at that was the end of it, is it true? don’t know, but I’ll sure miss them.
We ourselves offer a urlblacklist, as previously mentioned it’s not free, but we do provide free limited trial, or low cost for a limited volume test run for a longer time.