Dragon Master is a great filler game for two by Dr. Reiner Knizia. Like many of his other titles, the rules are simple: play your 8 dragon cards back and forth until you create a 16-card grid, then score! Of course, it's how you score your cards that makes this game more crunchy and tense than you might expect.
The theme is pasted on, but I love dragons! If I get to look at cool dragons as I play a game about numbers, that's a plus for me!