For small spills, sprinkle generously with salt while the oven is still hot. The salt absorbs the liquid content. The mixture will burn and when the oven cools will scrape off with no trouble. For thorough oven cleaning, fill a shallow dish with full-strength ammonia and place inside the cold oven. Close the oven's door and let it stand overnight. The ammonia releases ammonia gas(surprise!) which is slowly absorbed by the grease. The grease will turn into a soap-like goop which can be easily wiped off. Make sure that you do not use this method on aluminum as the ammonia will damage the surface.
