KeyboardSee has blown my mind. This simple app (called "Keyboard viewer" on the download page) is just so useful. Like most good apps, it has a specific purpose. This one shows you the layout of all the keyboard setups on your computer. I use Spanish and Portuguese setups a lot, but can never remember where the various accents and punctuation keys are. Three minutes with keyboardSee taught me all of them. Just seeing the keys laid out makes a big difference.
Don't forget that Shift/Caps Lock will show you new keys. And don't overlook the options down on the bottom. The Scale slider alters the size of the keyboard, and the Current button jumps to the keyboard layout currently being used on your system (in case it wasn't already there).
Since keyboardSee lights up keys as you type, you may even find it helpful for working on your type speed.