I agree with rare Sound hardware (i.e. Roland, GUS and AdLib especially) and rare Video Card hardware (i.e. Voodoo, etc.) being at the top of the list, but I have to say that Tandy 1000 hardware, whether it is expansion cards, accessories, or the various Tandy systems themselves are VERY soughtafter and seem to sell right away when they are at a reasonable price.
Despite not being a big fan of Apple, I have to also say that a lot of old Apple Macinotsh and Apple II stuff seems to sell for crazy prices as well.
I have to agree with PeterLI about IBM 51** hardware as well...seems to me be super hot the last few years as well.
*EDIT*...and is it just me, or is everyone and their dog into hardcore retro game console collecting now too?? I have always been collecting console stuff, but now it seems everyone, young and old, girl or guy, man or beast, is trying to get their hands on any game console they can...I used to find stuff in thrift shops all the time, but now there is usually just empty dusty shelves with crappy xbox (one) and ps2 sports games leftovers. I swear in the last few months I have been treating a lot of my old retro gear and console stuff like gold considering how quickly it's becoming rare. I have a feeling that a lot of the younger generation now is into retro gaming more that people from my (a bit older) generation ever was...I don't have any facts to support this notion but it really does seem that way.
Videos like this on youtube, where people have shelves upon shelves of games and retro hardware has become commonplace and does not seem to be letting up at all...
https://www.youtube.com/watch?v=FGb7ITQJfQ8
https://www.youtube.com/watch?v=uLuUDXlHPy4
https://www.youtube.com/watch?v=HdI8wdP0emo
https://www.youtube.com/watch?v=GTIoEWDfH_c
https://www.youtube.com/watch?v=pgNxBTww-ag
I always throught that serious retro hardware and game collecting would have taken a long time to catch on at a large scale, but I think I have been proven wrong over the last few years.
I think it's awesome that people are collecting though and I think interest in retro hardware is growing exponentially...that may mean that retro gear will get much more rare, much more quickly that I originally thought.
I wonder how hard it would be to pick up some of the older retro gaming hardware 5 years from now?