After looking for more than a year for the perfect stone slab to go in our main bathroom, I finally gave up. We used a slate tile on the tub surround, and it was impossible to find any natural stone slab that would work with the colors of the tiles.
Fortunately, the contractor who managed all the framing, electrical, and plumbing work for the remodel used to work with concrete back in the day. Recently he's gotten back into concrete work, specifically stained concrete and this new product called Granicrete. This stuff is great. They put a thin layer of this material over a plywood or MDF backing (or even right over existing tile), and in our case, they were able to texture it to simulate the roughness of our slate tile.
(Sorry about the glare from the bathroom lights!)
I gave him two pieces of the tile we used, and he was able to select stains that matched their color fairly closely. I specified that I wanted the countertop to mainly be tan, so he used a small amount of the gray/green stain to put what looks like a vein running through the countertop and backsplash.
They finished it off by pouring a self-leveling high-gloss epoxy over it. They let the epoxy just drip down the edges to keep the rougher look.
We're really happy with how it turned out, especially considering it was so easy to customize it and the price was just right (about half way between the cost of formica and a granite slab). Now we're kicking ourselves for using tile for the master bathroom vanity instead of doing this in that bathroom, too!