Where would be best to go depends largely on what sort of photography you prefer. From your list, I'd guess that you're more interested in photographing interesting cultures than in photographing landscapes. Is that true?
If you're actually interested in wild landscapes too, then October is a great time for New Zealand, which is a very beautiful, friendly and pleasant place (keep in mind that it's spring there in October). I've been to Thailand too (3rd on your list), and it was indeed interesting to see the very different culture there, but it was very hot and polluted, which makes it less pleasant (but the food was excellent ).
October would also be a good time for the American Southwest (Arizona, Utah, New Mexico, etc.), if you like that sort of thing (weird landscapes, "Old West" stuff, etc.).
Another thought: October is also a good time for Italy - the summer tourist hordes have mostly disappeared. Rome is fantastic if you like ancient ruins, historic architecture, and general atmospheric cityscapes, and there's so much there that it can keep you busy for the entire trip.
Lisa
