This page describes Loki’s electronics. My other robots use similar, with variations. So, most of the core info is here, but there may be details specific to each robot on its design page.
All of my robots use a main processor (laptop or PDA/Phone) for the higher level software, and a microprocessor for sensor interface, and often motor or servo control. Loki has a laptop embedded in his chest that communicates via USB to various electronics.
For the MicroProcessor, I have been using a PIC-based Mark III controller board, which used to be available here, but I have heard may not be available any longer.
1/15/2013 Update! I finally moved to Arduino! See Arduino section below.
(click on pictures for larger view)
Sensors and Control Block Diagram
PIC Interface Board
PIC I/O Expansion Board
Head and Arm Boards
Arduino Robot Interface Shield
Arduino Interface Schematic
Arduino Board layout, using a proto shield