We really liked these Apple Magic Trackpad stick-on decals, available from Killer Duck. One shows the gestures you can use on the trackpad, while the other shows the most useful Cmd+ keyboard shortcuts.
Killer Duck also produces some neat-o superhero decals for Mac keyboards. See the gallery below.
- Apple Magic Trackpad Shortcut Skin
- Apple Magic Trackpad Motion Shortcut Skin
- Macbook Keyboard Super Hero Skin / Vinyl Decals
- Macbook Keyboard Star Wars Skin / Vinyl Decals