If you’re a fan of “transport puzzles” like Sokoban or Atomix, or possibly even some of the robot puzzles in Sierra’s classic Dr. Brain series, you might love one of my recent online discoveries: RoboZZle. (You may be prompted to install Silverlight in order to play, but it’s safe, easy, and well worth the download.)
Solving the puzzles is sorta like programming a computer, so those of you with a mathematical or computer science bent will be more likely to enjoy it, but the programming environment is so simple (only “go forward”, “turn right 90 degrees”, “turn left 90 degrees”, and “only do this if the robot’s on a ____ colored square”).
So check it out, and let me know if you find any particular favorite puzzles. I had fun with one called “Tetris”, and I haven’t solved it yet, but I like the idea behind “Reflection”. (Both of those two are by the same author.)