Rate Your Music - a great place for music lovers.
del.icio.us - I put my bookmarks here so I can easily access them everywhere.
LibraryThing - the ONLY place for book lovers. I haven't been paying too much attention to this site lately, though.
MobyGames - for anyone who plays electronic games.
DVDProfiler collection - a good place to store your DVD collection.
ToffeeWeb - a site I started around 1993 and run for a few years. But if it wasn't for Michael the site would have died a long time ago.