Over on the Make blog, there’s a great list of a bunch of Arduino kits, books, and add-ons.
The Arduino open-source microcontroller platform can be programmed and equipped to perform a nearly endless list of functions. It’s likely the best all-around centerpiece to a modern electronics project. But one of the tasks Arduino is best used for is straight-up fun – the open design means there’s an Arduino board suitable for almost any project, and a wealth of add-on “shields” extends its abilities with ease.