I always have intermittent trouble with my bathtub drain from my long hair clogging it up, and I use the Zip-It drain tool. Just a long plastic flexible stick thingy with "teeth" that point back up toward you. It is truly disgusting the stuff that gets pulled out with that thing...

but then the drain works just perfectly. This is it:
http://safetycentral.com/zipitdrcltoi.html
It says $4.99 there, but I've found it for under 4 bucks at Ace Hardware. Mine usually lasts close to a year before the teeth just get worn out and I have to get a new one. Works great, and best of all, no smelly chemicals!