DialUsername :
Dial user name is a site username availability checking tool. It checks your entered username availability for around 50 user driven websites. It might not be dead accurate sometimes but still gives you the idea of most of the sites.Not only that, you should know that your username is your unique id on web. And nobody else should take it before you. Or they can even act that they use your name to get popularity and traffic. So your id only belongs to you and you can check if someone else is using it for wrong purposes.
Knowem :
KnowEm checks the availability of your brand name, user name or vanity URL on 120 popular Social Media websites. If you have money, it can also sign up for you automatically on all sites. The transaction will be carried through paypal.
Username Check :
As the name says, is a free online tool that allows you to check whether your desired username is available or taken on several websites almost simultaneously.
It is the most hardest thing to signup and check your username for all the social bookmarking sites. These sites have understood the case and given us the best solution. A time will come when the automated sign up will also become free. I'll wait for that !

