This is my first robot called Sandwich-3000, which is basically a line follower robot. It was taken from the popular book "Robot Building for Beginners" by David Cook. I think is a good book to start with. Theory is explained in a very pleasant and easy to understand way. I made it with off-the-shelf parts only, and if you do not want to wander around different places looking for them, there is an online store at Solarbotics.com where you can find the kit with electronic components and a very well made PCB for a reasonable price. My robot does not need a programmable chip. Instead, it uses the LM393 dual comparator that makes him decide where to go.
For sensors, it uses two pairs of cadmium sulfide photo-resistors. To make the wheel coupler easier to work with and mold, I used a plastic tube and a pair of plastic standoffs instead of metal pieces as suggested in the book. It was a fun project that I finished a couple of years ago and I think it will appeal to those who want to begin this hobby.