Here's a handy trick that's new to me, but familiar to at least two of my friends. I found it in the January/February 2008 issue of Vegetarian Times, which used to have a one-page section at the back called "Fridge Notes." If you need to UNCLOG A DRAIN, don't purchase all those fancy chemicals. Try this first! Unless your problem requires a plumber, this should work for you. (I have rephrased VT's instructions to reflect my own experience)
1. Pour one cup of baking soda and one cup of salt into the drain. (Key: make sure it actually gets INTO the drain, not just on top of the drain i.e. still in the sink bowl.)
2. Add one cup of vinegar and watch the fireworks! This will bubble and sizzle, perhaps for several minutes depending on how much the drain is clogged.
3. After waiting several minutes, add approximately one cup of boiling water. You may need more, depending how long it takes for what you've added to completely exit the drain.
This not only clears a drain, but also scours it due to the abrasive nature of the baking soda. Your drain will be unclogged, clean, and smell like...well, vinegar and baking soda, but that's not the end of the world! Best of all, you haven't used any dangerous chemicals.
Pass it on! And if you have any additional feedback/tips about this or any other drain-unclogging methods, please comment and share them!