Everyone probably already knows this one but its one of my faves and i did it just today...
An easy way to clean the microwave, squeeze a half of a lemon into a bowl with like a cup of water, and i actually leave the lemon in the water as well. Pop it into the microwave for about 4 minutes. Let it sit for two. Open the door and just wipe away the mess. The steam from the lemon water releases the tough food stuffs AND it makes the microwave smell clean