I don't often find stuff, and ever since I found a 24-shelf rolling paper rack for $5 (sells in stores for $50-$60) I haven't looked as hard because I don't think I could ever do better than that.
But sometimes I seek out sales that specifically mention having scrappy stuff, and I've gotten a few stamps and some nice paper that way. One time I also found a several-years-old kit that contained some journaling embellishments I'd bought and loved and used up years earlier, so finding extras of them (50c for the whole box!) was great.
These days, I yard sale a lot less (I don't need so much junk!), but I do love the scrapbook garage sales held quarterly by the local scrapbook store.