Last night at a family dinner party, we heard a lot of praise for a chemical-free drain cleaner that costs around $2.50, is made from a piece of thin plastic, and is said to work better than toxic chemical cleaners...
The Zip-It Drain Cleaner by Cobra is fashioned from a thin piece of flexible plastic with jagged edges, a sort of poor man's plumbing snake. It's thin enough to slide underneath a drain stopper, and it works particularly well on hair clogs. It's more eco-friendly and more effective than Drain-O, our only qualm being that the instructions recommend disposing of your Zip-It after one use. The company warns that the jagged edges can hurt your fingers (and the stuff that comes up isn't fun to clean off), but you could probably get a few uses out of a Zip-It if you use rubber gloves to wipe it clean. Zip-Its are available at hardware stores and other retailers including Amazon, Ace Hardware, Sears, and Lowe's.
For another non-toxic drain declogger you can whip up at home, see this post.