Brettspielwelt - the free, online boardgame portal
I live in Europe, I'm a geek, so I must also be a boardgame freak. I love games, and especially German style boardgames, with their intricate rules. Unfortunately, there's not much time to play, and not a lot of people that I can play with. Following a link on boardgamesgeek.com I've stumbled on this website, an online portal of boardgames that you can play, something similar to IGS (the Internet Go Server), but that implements loads of boardgames to be played in multiplayer style. The people are friendly and are willing to teach you to play (even in English). The client defaults to the German language, but this can be easily changed by changing the 'Nation = de' line to 'Nation = en' in the props file from the client download folder.
Being a Java application, it goes a long way to adding a few more entertainment choices to the ones available for the Linux platform, in terms of games.
UPDATE: There's a ton more of sites with online boardgames at the boargamegeek wiki
Some of these sites:
http://www.flexgames.com/ (2 games)
http://www.yucata.de/Default.aspx (several, growing)
games.asobrain.com (few, but has Settlers and Carcassonne)
http://www.spielbyweb.com/ (forum based)
http://yourturnmyturn.com/ (many, most classic)
http://hilinski.net/games/online/ (Taj Mahal and Tycoon)