Here's a great productivity utility that I didn't think I'd like, but after installing it and using it for a day, I'm strongly considering leaving it on my system. CornerClick allows you to configure any or all of the four corners of your screen into clickable areas to execute a series of different types of actions. CornerClick can launch an Applescript, hide an application(s), open a URL, or activate different Exposé settings. Right now I'm using it primarly as a way to hide applications with my mouse rather than a hot-key combo, but can see myself starting to use it to launch various Applescripts.
CornerClick installs as a System Preference pane. It's still in development and I've had it crash System Preferences.app a few times, but am willing to give keep it around and watch it mature. Very interesting application. Check it out.