This is wonderful!
I have to admit I was a bit skeptical and thought it probably wouldn't do a great job - wow, was I wrong! This required hardly any effort and got the bottom of my oven really clean (see below for my idea on cleaning the sides). It's absolutely non-toxic and non-smelly and requires little to no elbow grease!
1 cup baking soda
Liquid detergent or liquid castille soap (I love Dr. Bronner's)
Sprinkle or spray water generously over the bottom of the oven. Cover the grime with baking soda. Spray more water on top of the baking soda.
Let this sit overnight. Wipe up the baking soda with a rag or wash cloth - the grime/yuckies will come with it.
Squirt a little soap/detergent on a damp sponge to wipe up any remaining baking soda.
Since you can't exactly let baking soda sit overnight on the sides on an oven, I'd suggest making a paste of baking soda and water and wiping that on the sides. This should get the grime off with a little rubbing. You might also try adding some castille soap to the baking soda/water mixture to help out a bit.
I found this "recipe" on the Care2 website.