The Solar WobbleBot is a great little project for kids and other beginners. I love that it can be made entirely from recycled parts, and requires no soldering.
I do this project with teens (ages 12 and up) in my enrichment programs at schools and libraries, where it's always a big hit. It usually takes about an hour to make.
The Solar WobbleBot is one of the projects from my first book of robot activities, Robotics: Discover the Science and Technology of the Future from Nomad Press, for ages 9-12.
I also have a "Souped Up" version -- which uses a Miller Solar Engine to store energy, letting it work in low light -- in my book Making Simple Robots from Maker Media, publishers of MAKE: magazine.
Here's how to make the no-solder Solar WobbleBot: