I myself, is a chess enthusiast. I would always want to find a good opponent to play with, for competition and for fun. The level of my play is OK, but not really towards "skilled". But still, I can beat most starters.
The biggest free chess community would have to be Yahoo Games chess. Lots of people there. But there is one problem. Although you can play free chess, some guys there are very good, and some like to hog tables. They have problem clicking "Start Game", so sometimes you can hardly get a game going.
But the best Internet Online Chess out there will definitely be Ijji Chess. http://chess.ijji.com This site requires you to download the chess program but it is so beautiful and presentable! And it has many features, tournaments and it records your previous few games in a graph!
Pogo chess. Quite fun there too, but the interface is too beautiful, but not as friendly as Yahoo.
Flyordie chess. This site is quite good too. Waiting time is low. When you challenge someone or get challenge, the game is started immediately. Lots of players there. But there is one problem. The chess pieces are too "cute". Not like the regulars. You need to take some time to distinguish them.
64squar.es is a great ajax chess site where you can play against others and there is no time limit.
And if you haven't, try Freechess.org. It has a very big chess server with many people playing. Starting a game is really fast and easy.
There is a flash online chess game where you can play free chess. It is developed by FreeOnlineGames. I embedded it here. Have a look: