The BoE-Bot Robot Kit (USB) is a complete mobile robotics kit.
The BASIC Stamp Discovery Kit (USB) is a great way to learn the Basic Stamp.
The Parallax StampWorks Experimenter Kit is a comprehensive collection of everything you will need to learn about efficient embedded design. This is a great package for those who want ALL the accessories!
This board is a great starting platform for learning how to take advantage of the Propeller.
The PropSTICK is USB device which lets you access all the Propeller's pins on a 0.1" format.