I want to recommend the following sites to all that enjoy strategy games:
www.conquerclub.com - Over 200+ maps using the system from RISK. You can play up to four games for free at a single time. Moves are done with some days between. So joining and trying the site out is very little time consuming. Try not to join a game with "endless" settings. The fantastic thing about the site is the enormous varation of maps, rules and settings. If you get hooked... it's very cheap to pay for membership and then you can play maps faster or in teams. Win in a world war II scenario, explore South America or take over a prison! It's so much fun!
www.boardgamearena.com - A nice site to try different board games. Personally I like the following games here: Stone age (w/4 players), Puerto rico (w/4 players), Incan gold, Kahuna, Quoridor, Pylos and 1vs1 Carcassonne (international rules no/expansion). Both Stone age and Puerto rico are considered some of the best 4 player games ever made... when you understand the debt of them... need some plays. The site also features tournaments. NB! I had to use the Edge internet explorer to get the games working.
www.yourturnmyturn.com - Ranked matches in many 1vs1 games. I recommend Carcassonne (The castle)... a very nice game here. You can also join tournaments.
www.tribalwars.net - If you got some time on your hands and want to join clans and get some diplomacy too...
www.brettspielwelt.de - German site with some nice games