I've seen people with two torches, and I know the Tish's Tinkered Lanterns can stack (even if you have two of the same kind), so yeah, I'd assume regular torches stack too.
The torch. What a wonderful invention. I didn't know anything about it through my first 13 levels with my Barbarian Paladin. I had played with the gamma and found the game too dark. I am sure the matters were even more complicated being she started out in Freeport. What a dark depressing city. I had gone into a cave with a friend who was mentoring me and complained after letting the group die about how dark it was. I told him all I could see were the names. That's when he told me about the torch.
Yes, you can double stack the torches. They go in the same slot as the potions do though. It is a wonderful thing to be able to see when it is dark out.
I haven't had the courage to go back and play the paladin since I so badly wiped out the entire group I waa pulling for. Of course it didn't help that I was wildly swinging and hitting everything within the area and then not swinging because the beasties were in the wall. It was not a good showing for her and I know a few people who will never group with her again. Doh!