I spend much of my internet time gaming on RuneScape it is a massive multiplayer online role playing game, much of the other time is on Facebook and any kind of Wiki for the game I'm playing at the time for any kind of information I need at the moment. A list of most visited would be:

www.runescape.com (#1 Most favorite)
www.facebook.com
www.(game)wiki.com
www.youtube.com

Facebook of course is THE social networking website that most everybody uses.

I use the wikis for any information that I need at the moment for that game.

YouTube Mostly for music.