Is it metal/stainless or glass top?  I know it sounds odd, and I was surprised by it, but Lysol 4-in-1 All Purpose cleaner is pretty darn decent at cutting grease, even if it's been on there longer than we like to admit. I use it on my glass cooktop with gas burners, then polish with glass cleaner. Have also used Barkeepers Friend powder on it with good results. Since mine is glass, I've taken a razor blade to in occasionally chisel off the really crusty stuff. Wouldn't try that on enamel or stainless though, as it'll scratch pretty bad, I think.