* If you don't see condensation dripping under the car, check the drain tube.
* If you do see condensation under the car, turn the heater on full blast for a few minutes (I'm not kidding).
As pointed out, there's a smelly bacteria responsible for the stink -- but a few minutes of heat will kill it and eliminate the problem.
Remember one guy called a radio talk show about the problem -- and the idiot host told him he had a dead mouse somewhere in his a/c system. Imagine the wild goose chase that poor guy went on...
FYI: Just posted this on another thread.