KnowEm Username Check

I can never remember all the places that I've signed up for, so I found knowem.com a useful tool. It will check over 500 social media sites and 150 domain names for you to see if your name is taken or available. Useful on both a personal and organisational level. However, if you don't like this one, try Namechk which gives a single page result on over 150 social media sites.