This is the easiest way to clean a microwave, in my opinion. No scrubbing required! An added bonus is that there are no chemicals involved. All you need is half a lemon.
Cut the lemon into a few slices and place them in a microwave-safe glass bowl with about 2 cups of water. Squeeze some of the lemon juice into the water and then toss the slices into the bowl. Microwave on high for 5-10 minutes. Do not open the microwave after it's done. Leave the door closed for an additional 10 minutes. Then, take a paper towel or cloth and wipe everything down. All the stuck-on nastiness should come off very easily and it leaves the microwave smelling lemony-fresh.