I am officially recommending Qwirkle as a great addition to any classroom. I recently played it with my students after borrowing it from our Gifted and Talented department. It is a great game, and it challenged the students without being overly difficult. It doesn't take long to learn, but Qwirkle will take a while for the students to master.
Gameplay: The game is made up of tiles; each tile has one of six shape, and the shape is one of six colors. The goal is to build onto previously made sets by joinging columns and rows that contain only one attribute (shape or color) in common. I will leave it to Wikipedia and YouTube to do the explaining of the rules in more detail.
The game plays similar to Scrabble with people trying to win points by creating and joining sets of tiles. Overall it is a great way to spend an indoor recess period or quick 30 minutes of free choice time. I wouldn't hesitate to say that this game belongs in the game closet of any teacher.