I would do a stacked stone tile on the part that jets out from the full wall. And then some sort of coordinating marble or granite top that hangs over the edge a few inches on either side. Lights under the edge of the counter (maybe like a rope light or something) to cast down and accentuate the texture of the tile.

I think you have a good idea. You could paint the drywall one of the colours in the slate and do a slate top.