UserNameCheck.com > Review by hispanic
Rocks
Michael Scepaniak
Nov 24, 2008
This is just a simple service that does pretty much what you would expect it to do. I think sometimes it is prone to returning false positives (flagging a name as "taken" when it is actually available) and it doesn't include FaceBook, but these are small complaints for a free and easy service.
I _do_ wish, though, that it would recognize when a name is illegal for a given service (e.g., names that are too long for twitter or contain illegal characters for YouTube).