I don't own them anymore, but vintage Hewlett-Packard calculators, the RPN variety for engineers. An acquaintance moved into hospice a few years ago, and his family cleared out the house. I went over because they offered us sailors pick of his old boat gear, but I poked through the pile of electronics destined for the recycler, too. I grabbed several old calculators, a printer unit, and some programming books for them, as I was vaguely aware that maybe some people collect them. As it turns out, I got almost $700 for them on eBay.

The ones that I do still own are several IBM Model M keyboards that I picked out of the $1 keyboard bin at the university surplus shop back in the day. Although, after using one of them for 17 years (with no signs of wear), I realized that 5 spares would long outlast me, I sold a few for almost $400 total.

Another friend unexpectedly passed away earlier this year. A neighbor is helping to liquidate his vintage computer collection. I stopped by the house and saw a Northgate OmniKey Ultra in a pile, and asked how much would he take for it. Turns out, that was a recycling pile, so he just gave it to me. I could probably get $200 for it after cleaning it up, if I didn't need it.