I use baking soda and crumpled up aluminum foil....seems to work ok for mine. It's a little bit of scrubbing but seems to be the only thing that works for me.
I throw mine in the dishwasher on a regular basis (say once a week) to keep them from getting cruddy. If they're really messy I'll soak them in water for a bit and then scrub with a little OxyClean.
Re: Cleaning stove burner covers