I did a kitchen reno about 7 years ago and was really happy with the selection at this place:
http://www.imcstone.com/They have a massive warehouse you can walk through and see all the individual slabs so you can know pick exactly the one you want if they have multiple from each lot.
Their policy may have changed since then, but the only thing about them I didn't like was that they wouldn't give you pricing unless you were a contractor. They would only tell you what "grade" the slab you liked was and it was up to you to negotiate the price with your contractor. Hard to feel like you're getting a good deal in that situation.