Arduino is a low-cost, easy to work with PIC programming system. You simply plug it into your Mac or PC and using the Processing-like IDE, write programs for it, click a button, and it downloads the code to the board where it just starts running. Very simple, very easy to use, very fun.
I bought my board for about $32 from Spark Fun Electronics, and then hit Dirty Ernie's to get some cheap resistors and such to make it all work.
You can find out more information about the product itself on the Arduino website.

Projects - Miscellaneous
Here's just a quick list of some sketches I've made thus far:
Scott Lawrence