One of the reasons I got some of these little kits for Christmas was to work more on soldering and construction neatness. Today, I assembled this Velleman Running Microbug (MK127), purchased from Electronix Express. I did this with three kids and the new puppy all playing around me - something I could not imagine doing a year ago.
I don't know why it amazes me, but, it worked the first time. The Microbug chases light with its two open chassis motors. Light sensitivity can be adjusted with the two pots on front and the LED "eyes" indicate driving direction. It runs on two 1.5V AAA batteries, can be switched on and off and stops moving in total darkness. The assembly instructions and a schematic are here. This little kit is only $12.75.