Do you accidentally press the Caps Lock key all the time? If so, the Capster is exactly what you need. This easy to use application will tell you when you pressed the Caps Lock, either on its own or through Growl.
Capster v2.0 MacOSX Retail-CORE
When you press the Caps Lock key, Capster's menu bar icon will change as well. For touch typists this is a great way to keep your focus on the screen.