The website: free internet chess server
http://www.freechess.org/ This website usually has a few hundred people online. I have found it a lot better than Yahoo because:
(a) They usually randomly choose a color, unlike yahoo where host always chooses color. They do have the option of choosing a color, but almost no one uses it.
(b) They don't have blatant abuses like yahoo chess. I remember one time on Yahoo I was winning a game and the host kicked me out of the table.
(c) They don't have that annoying feature where you can accidently walk into a game and take someone's seat, and the only way to exit is to resign that person's game for them.
(d) There is more Blitz than standard, but it is easier on this website to find normal time control games than on Yahoo. On Yahoo everyone seems to play 1 minute games, especially the people who are "2000+". On ths website, you can still get some longer time limit games.
(e) This website has about 20 or so free lectures which cover opening and endgames topics, and some tactics. These are pretty interesting to watch.
(f) Games are adjourned. This is an advantage because if you disconnect, the game is saved for later. Sometmes, my modem disconnects for a minute or two and then reconnects and I continue the adjourned game. I'm pretty sure on Yahoo I would just get a bunch of losses because of my bad connection.
There is also ICC, but you have to pay to join that.