Each year, my wife and I buy one game to had to our game closet. (We are also planning on buying Dark Ages, hooray!)
Here is our shortlist of potential games to buy:
citadel
power grid
King of Tokyo
Race for the Galaxy
I know there are list of other games out there, but our specifications are kinda unique. Let me explain.
We currently own: Dominion, Carcassonne, Bang, Ticket to Ride, Small World, Pandemic, Wizard and Killer Bunnies. Of the above we most often play Dominion and Carcassonne followed by Ticket to Ride and Pandemic. We typically enjoy games with a shorter playtime (30 minutes) so that we can get in a couple of games on a Saturday night. We like Small World, but have found it takes too long for us to really like it. Bang and Killer Bunnies we play with large groups of friends who aren't quite as into gaming.
Mostly we are looking for a game that can be played in ~ 30 minutes. works for 2 players. and has a dynamic different from the above mentioned games.