After google now Facebook is coming up with vanity urls. It will be from June 13th onwards.

So Login with your user name and password on the page http://www.facebook.com/username/.  Now there is a count down, when that is over you can register your username. So do it fast otherwise you may not get the name you are looking for.

Here is a list of names that are already gone

Here is a tool by Amit to check the availability of the name