I watch out for printer ink cartridges at yard sales - people will change the printer and then just discard the old cartridges. I've managed to sell a few on EBay in the last few months.

During the summer I found a couple of bags of what looked like just yarn at a yard sale. Paid $12 for the lot. When I emptied the bags there were some weaving shuttles and some amazing yarn in there - I kept a fair bit of the yarn and still realised about $50 on EBay.

The most recent find was at the Salvation Army thrift store. A bag of interesting yarn for $5. Turned out to be about eight skeins of high end yarn - silk, alpaca, mohair and some of it hand painted. Some of the skeins still had prices on them - anything from $18 to $29. I'll be putting some of that on EBay fairly soon but keeping some for me. What gets me is that is was clear from the pricing what they had and yet they stuffed it all in one bag as a job lot and sold it as cheaply as they did the cheap acrylic stuff in the same bin. even if they wanted to make a quick sale I'm sure that they COULD have got more for this stuff.