I bought a new MacBook Pro the other day and being the geek that I am I have completely immersed myself in Mac stuff and almost have it fully personalized. Here's a dashboard widget that I found that is not only totally lacking in practical applications but it's also one of the most clever widgets I have yet to find. The Carpenters Level Dashboard Widget makes use of the sudden motion sensor built into the laptop to drive a graphical carpenters level. 

On a serious note, the Apple Dashboard function is growing on me. Once you get past the trivial weather and clock widgets that is. I have a widget for posting to my blog and monitoring my gmail inbox, among others. In many ways this is the realization of the AJAX desktop concept, and Yahoo!'s Konfabulator but with a nice and seamless integration with your desktop.