You've Got Maids of San Antonio has tips for getting rid of garbage disposal odor:
If you feel your home cleaning has been for naught because of unpleasant odors coming from your disposal, cut a lemon or orange in half and toss them in 15 seconds apart while running cold water (be sure to not use your fingers to press the fruit through the rubber drain!). The juices and oils from the fruits naturally clean the walls and blades and leave a fresh, long-lasting scent.
Fill an ice tray with vinegar and wait until frozen. Upon freezing, run them through your disposal two or three at a time with cold water. The ice helps scour the walls and sharpen the blades and the vinegar will safely destroy odor causing bacteria.
For stubborn odors, pour two heaping tablespoons of baking soda into the disposal and let it set for at least an hour (two or three hours would be ideal). Rinse away with cold water and drop in a lemon half to leave a fresh scent.