Robot kits, parts, and microcontrollers
Parallax Inc. The makers of the BASIC Stamp, they have microcontroller starter kits and tons of sensors and other addons.
Jameco Robot Store Owned by Jameco electronics, they have tons of components and have had tons of robot kits and microcontrollers since
they started which was before they were owned by Jameco.
Lynxmotion They sell tons of different types of kits and microcontrollers.
PAGERMOTORS.com They have a few BEAM kits and a purdy good bit of parts for building BEAM bots.
The Robot Store A really good place to find kits, microcontrollers, other electronics, and tons of other stuff.
E-CLEC-TECH Has a fare mount of anything electronic or mechanical. They have microcontrollers, motors, other electronics like parts,
and tons of other stuff.
eBay Yes, eBay is a good place to find tons of robot stuff.