yiid - yiid - Your Internet Identity - Simplify your community life
Instant Username Search - Check out if your username is available
Profilactic - Profilactic.com is an online identity aggregator that pulls together all of the profiles and...
Namechk - See if your username is available on 100+ social networks
humanID - humanID is a one-click anonymous SSO that provides users with an anonymous identity layer.
Handlescout - Get notified when a Twitter username becomes available