Namepedia, www.namepedia.org

The real people section is really nice with all the related people. I could not remember that Spanish tennis player name, looked up Roger Federer, and there he was (Rafael Nadal).

They have accurate info about given names and surnames. Every name has a description, variants, related famous people and usage information. You can use it for getting info about your name or for finding your ancestors. The name database contains tons of forenames from around the world with gender, origin, languages, etc.