Baking soda is a miracle worker. I always take the fridge box out the day of our vacation and dump it into the kitchen sink drain. I don't come home to a stinky sink.
For people with disposals, I also will grind up a handful of ice cubes every so often. It helps dislodge all the nasty encrusted gunk that can smell bad. If you've ever had to go fishing in the drain for the fork your husband put in the wrong side of the sink (after being requested not to do this at least 800,000 times) you know what I mean.