What are some other social media/networking sites other than the "big" ones like Twitter, Myspace & Facebook?

Does anyone know of any good social networking sites besides the big ones, Digg, Twitter, Myspace, Facebook, Linkinden and StumbleUpon?

Thanks

For sites like myspace, facebook, hi5, check this wikipedia category:
http://en.wikipedia.org/wiki/Category:Online_social_networking

For sites like digg, stumbleupon, check this category:
http://en.wikipedia.org/wiki/Category:Social_bookmarking

If you need more categories check this other category:
http://en.wikipedia.org/wiki/Category:Social_information_processing