FREEPersonalBlock is a new browser extension for Google Chrome, Firefox and Internet Explorer that lets you selectively block entire websites from your search results when you're searching with Google, Yahoo! or Bing, getting search results that had little to no value. For some added fun, try the same search on a different search engine.
FREEThis app allows you to block search results from Google, Bing, Yahoo, Ebay, and Criagslist (with more to come). If you block on one of the sites, it will block on all of them.