BackTweets is a Twitter search engine that allows you to do one thing: find out who links to a specific webpage or website on Twitter. All you have to do is to enter the specific URL you want to check and backtweet will show who is not just talking about it but linking to it.
Backtweets is pretty cool because it does a good job of determining who links, even when there are so many different URL shorteners out there. Note that you can also grab the RSS for your search result so you can monitor the incoming links in your feed reader.
For added goodness, you can add backtweets as a search plugin (if you are using firefox) so you can do a quick search without assessing the homepage.