I won't need to say much about this video from hilaroad.com that shows how to build a simple electric motor because it is so well-made and comprehensive. The video shows you step-by-step how to go about making a simple battery powered motor. This is a great rainy-day project, party trick, and desktop conversation starter. I've made one myself and the results -- even though entirely expected -- are mysterious and somehow thrilling. You really should try this when you have 20 to 30 minutes (tops!) to spare.
The video also covers the basic theory involved in electromagnetism, which includes the disassembly of a small toy motor. It all makes a lot more sense once you've made a small motor of your own. Other versions of this simple motor have you strip the varnish off the wire on only half of one of the wires. This makes the jump to understanding the commutator a little easier.
If you feel like getting the various materials together would be a hassle, you can always spend a couple of bucks on the Simplest Motor Kit. This would be good option if you want to send one to someone by mail. Though the included explanation book is said to be confusing, if you use it in conjunction with the video shown here, everything should be clear.