Do you like to play games? I have a few on my kindle that I enjoy playing. The two that I enjoy the most are Cubistry and Sudoku.
Cubistry is very addictive. It's a 3-D cube matching puzzle game. There are two different game modes you can play in but I always do the puzzle mode where you race against the clock to beat your record time.
My fastest time so far is 4:39:43. I'm finding that very hard to beat so I don't even try any more.