I looked at tile for months, and finally went with some granite (emerald green, I think is the name of the color) from HD, the 18"x 31" sheets that they sell for countertops. I got it at a substantial discount by buying it on sale and got an additional markdown on some of it because of minor edge damage, not acceptable for countertops, but which I turned to hide under the stove. The hearth's got a 470# stove sitting on it, and is doing just fine.
It took four sheets of the granite, three side-by-side, the fourth cut into thirds and lined up to extend the 31" dimension to about 42", so the finished hearth is 42x52, plus trim. Stacked it on plywood, micore (because of insulation needs for this stove), durrock, thinset, and the granite, trimmed out w/the cut-to-length stock oak trim at HD. Took forever to figure out what I wanted to do, and could have used an extra pair of hands, but for my first tiling project, I think it turned out nice (no pix, so it didn't happen, I know . . . )
The granite works great as a heat sink (warm buns AND warm toes), looks good with soapstone, and reflects the light from the fire. I I floated it on some cardboard to get the trim and hearth's height to match. Not fastened down per code, but I don't think it's going anywhere on my watch . . . You can also find granite there in smaller square tiles for not-too-much. They're real proud of their big pieces and the prices on that are through the roof, but if you get it in smaller chunks, it's not so bad. If you've got a cast iron stove, I think solid black granite would look, well, hot. There's some that has reflective blue flakes in it that would be pretty amazing as well. It's not top-of-the-line granite, but then I didn't pay top-of-the-line prices for it, either, and I'm very happy with it.
