When you think up that perfect new handle for storming social networks and other registration-only sites across the web, run it through UserNameCheck.com first. This webapp's purpose is simple: to tell you whether or not that name is already in use at a pretty impressive list of sites, from Delicious and Digg to eBay and Xbox Live. The developer explains:
This site is a quick and dirty solution to a question that I often lay awake at night worrying about. Do I have my username registered across every site that I should? What if the next internet humiliation meme just happens to share the username I've been using for years, and suddenly people are emailing me asking "hey, is this you ???". The site is simple. I have a stack of web app urls, the application pings the site using the username you want to check, if it returns a "no user name" error we return that.
The list of checks can take some time, so grab a cup of coffee or browse the news in another tab while UserNameCheck does its thing.