Thank you all again for the advice. Basically, these are pics of what I ended up with. What follows is the story of how I came upon them, so no one needs read it, but this is what I found.
I went to a couple of granite/marble places and right away, first place I go to, I find the Grinch that stole Christmas. Don't get me wrong, I had every intention of paying for whatever I could find. But the Grinch says to me she has to go outside and see what they have. I told her it didn't have to be anything special, not even a regular shape. She comes back and tells me she can cut me a piece from scrap unfinished granite 2" thick 2'x2' for $250! She says it would be cheaper if I would take marble 1 1/2' thick 1'x1' - only $150! I asked her if they had any broken pieces, anything they were throwing out I could buy and she tells me this was scrap she's talking about, they sell everything. I said thank you no problem and left. I don't begrudge anyone trying to make a buck but this seemed a bit off to me considering I could buy a perfect 1x1 from tandy for 50 bucks or something.
So I find another place not far from here. I go in and the woman really doesn't look very happy. So I figure - ok, ask because you're here and get out before you waste too much time with the second grouch. So I ask for a small piece of scrap granite, marble, whatever they have. She says to me; "you mean you want me to cut you a 1 foot square from one of my big slabs out there?" I said: "No ma'am, I just want something you might be throwing out" (I'm always nice because you never know). So she asks me if I'm looking for a broken piece? YES! She tells me go take what you want from the dumpster out back. Man, if I didn't feel like a kid again, and all for a scrap piece of granite, or marble, who cares. I'd take whatever at that point.
So, I go back there, and not to be greedy or dawdle before someone came out back and told me no, I grab the first 2 pieces that look reasonable and take off. As I was getting in my car, I decided I had to go back in and thank this woman again, and I think I surprised her by going back in there just to say thank you (especially because it's about 2 degrees out today) but it made my day when she smiled.
They're a little smaller than what everyone here was suggesting, but I didn't want to dig around too long so I grabbed the first thing that looked decent. If I decide to try and find something bigger later, I can spend more time looking since I already have something to use if someone chases me away while I'm looking through their garbage
The white marble has some scratches on it (it was in a dumpster after all) but I think it's ok for leatherworking, no? The surface on the black one is pretty clean, and I'm pretty sure it's granite, but I don't know a brick from a paver, so doesn't make much difference to me.
So what do you all think of my score?
PS. I'm pretty sure they're sink cut-outs so that's probably about the size they all were in there.