Any and all non-repetitive resources for learning embedded programming should go here.
I'll start us off with the obvious.
The Arduino is an extremely inexpensive microprocessor with plenty of I/O pins to do everything you'd want.
http://arduino.cc (note: They don't sell the product; you'll need to buy it from a supplier.
My recommendation for beginners: Buy a pair of Arduino Duemilanove microprocessors. 95% chance you'll burn one by accident.
For the more advanced user, you might want to learn more about how the arduino works by making one yourself
. You get the components and a breadboard and wire it up. This may even be cheaper than buying one! Though obviously less useful.
You can buy an Arduino starter kit from adafruit
. Not terribly expensive, either.
Ladyada is a site run by a very competent ... lady (as the name would imply). She has a huge amount of projects and kits for sale on her site (with full-picture instructions for soldering, etcetera.) More useful projects include the MintyBoost, the XBee Arduino shield, the protoshield, and the motor controller / motor shield.