My favorite way to clean my microwave is so easy and doesn't take very long, so I'm sharing my method with all of you!
Take 1/2 cup water and 1/2 cup lemon juice (You don't have to actually MEASURE this, just eyeball it), put it in a 2 cup container (so it doesn't boil over and make a bigger mess). Put it in the microwave and boil it until you have a good rolling boil (usually takes mine about 3 to 3 1/2 minutes), Stop microwave (DO NOT OPEN THE MICROWAVE) and allow to set for 15-20 minutes (or longer, if you don't get to it right away, it's not a crisis). Open the microwave, remove lemon juice/water, and wipe clean with hot water (you may possibly need a bit of dish soap, but shouldn't need any harsh cleaners).
I don't know HOW it works ... something in the lemon juice steam, I suppose, but it works and my microwave is clean without chemicals in my microwave!