Online Go Servers

Kiseido Go Server(KGS): The most popular go server in Europe and America, and in my opinion the best. Here there are many teachers that will teach for free, especially beginners. On Kiseido there are many chat rooms, and it's possible to chat with others while watching games. There are usually 1000-2000 people online.
Internet Go Server(IGS): IGS is a big go server where there are usually about 3000 people online. The chatting options aren't as great as on Kiseido, and it's hard to find teachers. However, there are often professionals playing on IGS, which is very rare on KGS. Also, if you dont like to chat, IGS may be a better choice, since on KGS you are expected to say "hi" and "thanks" at the beginning and end of your games regardless of you winning or losing. If you dont do this your opponent might get upset.
Wbaduk: Wbaduk(Previously known as cyberoro) is a Korean go server that also has an english interface. Last time i played on cyberoro, the ranking system was pretty messed up. You could find many good players being ranked low, which made it hard to find good matches.
Tygem: Tygem is the biggest Korean go server. To play on Tygem, you must know Korean, since it doesn't support any other language. Tygem probably has the strongest players out of all servers. This is because Korea is known for having the strongest amateur players, many of which who can, and has beaten top pros.
Yahoo!: You can also play go on yahoo!. There are not nearly as many players here as on the above servers (usually 100-200 people), and it's hard to find games when you're new since most players want to play against people with established ranks. Also, there are many rude people and escapers(people who leave the game without resigning). Even though there are not that many players on yahoo!, the level of play is quite high.
Fly or die: Fly or die is a website that has a lot of games, including go. On fly or die there are about 30 people playing go at any time. The playing level here is ridiculously low, most players being around 30-10 kyu. It's rare to see any dan-level players on fly or die. There is only one board size to choose from, which is a 15*15 sized board, and the time limit is always set to 40 minutes for each player, but players almost always use around 5-10 minutes.
Dragon Go Server(DGS): This is another popular place to play go. What makes this website different from the rest is the great amount of time given to the players(The default value is 90 days). You can also play many games at the same time. This makes DGS perfect for those that don't have time to sit through a whole game. It's also good if you want to deeply analyze board positions since you can download an sgf of the game, and use your time figuring out where you want to play the next move.
Online Go Server(OGS): Online Go Server is a turn based server like DGS. There are many tournaments on OGS to participate in, including 5 "title" tournaments.

You can find news for different servers at this website.