Namechk is a very useful online service which is a one place to check to if a username or profile name is available in many social networks /domain names.
Best thing about Namechk is you can check to see if your desired username or vanity url is still available at dozens of popular Social Networking and Social Bookmarking websites all at one place.
Namechk is extremely useful if you planning to start a brand, website or any related service by checking the username which you plan to register for your domain name, Facebook, Twitter, YouTube, LinkedIn, Myspace, Flicker and many more.
Namechk is a free online service which is also available on ITunes.
Learn more/Check it out: Namechk.
Hope this helped,do comment.