First try a Zip-It - »zipitclean.com
If that doesn't work, try drain cleaner, but after waiting the specified amount of time, flush the drain and use a plunger.
Keep pouring hot water down the drain (I repeatedly fill a large spaghetti pot with hot water) and plunge vigorously. Do it multiple times! If this is a tub shower, be sure to tape over the overflow hole.