You want to be VERY careful w/what you use for this purpose. As OFIC said, if you use the wrong 'material', you'll end up damaging your countertop anyways.
If you visit Kitchen Stores, like Lechter's (in my area), you're BOUND to find some 'ideas' on what you can use. As yet another option, you can 'install' a LARGE ceramic tile square (or 2 or 3 or ...) right INTO the countertop. In short, the amount of 'space' for the tile(s) would be kinda 'cut out' of the countertop, and tiles would be put in their place. It does look nice! If you do this be SURE to get tiles (or install a tiled area) that's a little LARGER than your biggest pot (or pots.) This will keep the heat away from the 'edges' of your tile, thus, keeping the heat away from your countertop.
My best to ya and hope this helps.
Jay J -Moderator