I mentioned this clever little app in my MacBook Air review yesterday as the way I got the F4 key to default to launching Dashboard again (instead of Launchpad). But it deserves a link of its own.
FunctionFlip is a background utility app that installs as a preference pane and it lets you “swap” the special keys back to regular F-keys on a key-by-key basis. Apple lets you do this in the keyboard preferences pane but the only option is to swap all the F-keys or not.