Mostly vintage electronics, (PC, cassette decks, VCRs, a laser disc player one time), cassette/Video tapes, I have about 1,000 NOS vacuum tubes I need to go through. I also like to sell car parts, but I don't go out of my way to look for them.
I kind of just like fixing that kind of stuff as a hobby, but don't really want to be a hoarder. I also find other oddball stuff once in awhile like really rare books or collectibles like vintage toys. It's all usually stuff that is hard to find so the people buying it are really happy to find it.