A number of people have recommended Stone Source to us lately. Built primarily as an online resource, Stone Source now has showrooms popping up all over the country which give you a really nice opportunity to see/touch/feel what you want for your bathroom, kitchen or whatnot.
Stone Source sells A LOT of stuff besides stone. Here's an incomplete list: granite, marble, limestone, ceramic, metal and glass tiles, stone, porcelain and gypsum. All of this is viewable on their intense website, which also allows for sorting, browsing and search.
We don't know yet how their prices match up to others, but we imagine they're competitive since Stone Source is dealing in volume. They want to be your one stop shop for all your STONE needs.