Most important GO sites

Most of you might already know these site, but I'm pretty certain that there will be someone who has missed some of them, so here comes the list:

Sensei's Library: it's a wiki page only for Go, if you want to know something about Go, it's there! If you don't find it there, it might not exist.
Go Teaching Ladder: you'll find reviews of games made by all sort of players, from pros to 30kyu. You can also submit your games if you want them to be reviewed.
Go problems: a huge collection of tsumego (go problems) to solve directly on your browser or to download to your PC.
Rec.games.go: this is THE Go group. Nice amount of activity and antiquity too.
Go clubs: a list inside Sensei's where you can find your nearest Go club.
Go servers: there are many of them out there and you only need one of them to play, I'll point some:

• Kiseido Go server (KGS): Lots of players, ranking vary too much, friendlier people, nice interface.
• Pandanet (IGS): nice interface, lots of players of high ranking, I had some trouble while registering.
• Cyberoro: I haven't tried it, though I've heard good reviews from friends.

Go Base: A list of professional Go games and players. It has a database search engine for searching through the collection and includes an online replayer that can display the games found in the database. It's quite difficult to register as they ask for non-free email account and verification from your Go club.
Go Discussions: a forum about go with thousands of users and lot of activity. You can also find reviews of Go software and equipment.