BoardGameGeek

BoardGameGeek.com is the biggest online boardgame community. And probably has the biggest Game Ranking as well. Over 5000 games (not counting expansions) are listed ranked; the database itself has over 40.000 games...

Games are ranked when 30 users rate a game. For more specifics on the methods used: see here. Of course, BGG users all have their own ideas on the system, but with a community this big, you can't please all. Moreover: if you don't like user ranking, don't use them.

Games that have been number 1:

Agricola

Puerto Rico

Euphraat & Tigris

Paths of Glory

Monkey Auto Races (April 1st Joke)

Game of Life (Testing the system)

BGG Top 10, July 10, 2009

All Games

1. Agricola
2. Puerto Rico
3. Power Grid
4. Twilight Struggle
5. Through the Ages
6. Dominion
7. Euphraat & Tigris
8. Le Havre
9. El Grande
10. Caylus

See all games: BGG Rankings

War Games

1. Case Blue
2. Combat Commander: Pacific
3. World at War: Blood and Bridges
4. The Devil's Cauldron: The Battles for Arnhem and Nijmegen
5. DAK2
6. Twilight Struggle
7. Lobositz: First Battle of the Seven Years War
8. EastFront II
9. Conflict of Heroes: Awakening the Bear!
10. Napoleon's Triumph

See all games: BGG Wargame Rankings