Chances are if you've got a hamster, guinea pig or similar-sized pet, it's living in a plastic cage you picked up at the local store. But if you've got time to kill over the break, you could build an awesome hamster run using stuff from your local IKEA.
At IKEA Hacker, Martina details how she constructed an elaborate hamster run based on the Expedit bookshelf. Hit the post for full details on how to construct the run, which is designed to provide entertainment for owners as well as pets: everything is at eye level.
Expedit hamster home [IKEA Hacker]