Dominion is the game that started a new genre:  Deckbuilding.  Winner of the Spiel des Jahres in 2009 and many other awards, Dominion has established itself as a true classic.  With more than a dozen expansions currently available, players will always be able to find new challenges.
 
If you have never played Dominion before, start here with the basic game.  There are millions of different combinations that can be played just with Dominion alone.  Each game is different but only lasts 20-30 minutes.  Great for two players but just as fun with more players.