Let me offer a few less common board games that are incredible for two players. Some of which are also very fun with more than two players:
Lost Cities - a card game where you choose carefully which explorations you want to invest in.
Carcassonne - a tile drawing game where you build roads, cities, farms.
Ticket To Ride - three different versions - collect cards, build train routes across different maps.
Transamerica - another train game, this one slightly simpler, connect a set of cities, one in each region.
All of these play under 1 hour with two players, some play even faster. And they have much more replay value than most games.
I also will second the recommendations for Chess, Scrabble and Backgammon.
--Jeff Abramson, co-owner Rainy Day Games, Aloha OR
www.rainy-day-games.com is a full line game store.