Well, Fallout 3 was the best in the series, I say, and Skyrim looks legit. If you have a crappy Computer, I would recommend the game "Chime". It's like Tetris, but with multiple songs, and grid shapes.
Your computer might be able to handle Portal, though, and that game isn't too expensive. It's one of my favorite games, too.
Team Fortress 2 is now a free to play game, and it won't be too hard on your run-of-the-mill computers, so I would recommend that too.
That's about all I can think of that you can run. Without knowing your specs, I mean.