For $4+ at Amazon. Works very well for ovens, grills, etc.
I especially recommend using Easy Off for cleaning gas grates. If possible, take the grates outdoors to minimize exposure to fumes and place them on a large garbage bag. This will help protect surrounding surfaces from the harsh chemicals.
Spray generously and let the product sit for about 20 minutes. Then, scrub with a steel scrubber and wash thoroughly with dish soap.
Note: While highly effective, Easy Off is a strong cleaner. Always use it in a well-ventilated area and wear long cleaning gloves to protect your skin.