My mom told me about this, its amazing how great it works. Moms Do know best!
If you have a pan (or stovetop cover, bbq grill, etc etc) with baked on grease, put the item in a plastic bag with a cup or two of ammonia. Close up the bag tight and let it sit for a few hours (overnight for really bad grease). WHen you take it out, wash with soapy water and just lightly scrubbing will wash away all the baked on mess!