Tumblr - take a look. There have been succulents, alliums, tuberous begonias... This time last year I noticed something else people were starting to throw out - their Halloween/autumn harvest decorations - mostly bales of hay. Last year I picked up four or five bales of hay that I was able to use in the garden and for the chickens. It was a little bit of a windfall, but I'm not getting my hopes up. I have been looking around, trying to see who has fall decorations that they might be getting rid of soon. I didn't think about this last year, but I imagine that people will be discarding other items as well, specifically pumpkins, winter squash and the like. I wouldn't pick up jack-o-lanterns - only whole fruits.
I expect that after Thanksgiving people will getting rid of fall decorations in favor of Christmas ones, so in the next couple of weeks, I'll be keeping my eye out for these things.