I don't have any Must Have's, I've already had a Compq Deskpro 286, Compaq Deskpro 386, many PS/2s, a holy mountain of old 286, 386, and 486 Laptops, and piles and piles of whitebox stuff from 8088-Pentium D.
As far as Branded equiptment goes that I'd love to have (but don't have the room for), IBM, GEM Computer Products, and 1989 and older Compaq tops my list, in particular, XT and AT style machines. However, IBM PS/2's no longer have a good source for reference disks, GEM's old desktops are very hard to get (as they are a local store to Georgia), and Compaq stuff tends to be missing keyboards, and the DSM monochrome monitors and EGA displays for them are hard to get. If I got any one of those three, I'd love the original hardware that went with it just to have a fully vintage accurate machine.
I also dig Tandy's 1000 and professional lines from the mid-late 80's, and have a Tandy 1000 myself that's souped up.
My Must-Keeps of the vintage stuff I have now....
- My Hot-Rodded 486 Setup - This thing is years and years of experience in dealing with 486/Windows 3.1x level computing put together the best I know how, and is configured as close to modern as possible....it even has a CD burner in it. But it does all of it's "modern" work under DOS and Windows 3.11 for Workgroups. Has a SoundBlaster AWE32, a 2MB S3 Graphics Card I'm trying to replace with a Mediavision ProGraphics 1280 that I'm having a b**** of a time finding the drivers for, Iomega ZIP. I'm toying with putting the Hard Disk caddie in it so I can make use of all my old sub-540MB HDD in it by making different machine configurations based upon year. If not I may take one of my old ATA hard disks of 40GB or so and multi-boot it to multiple O/S that will run on 486 hardware.
- The GEM 286 - This thing is a beast of a 286 both by size and power, I need to look into finding a 286 compatible bootloader and putting a Protected Mode based O/S on it like Xenix or early OS/2 to make full use of the massive 6144KB of RAM it has. It even has the 287 in it (an ITT 80c287), is overclocked to 12MHz from having that installed, has graphical internet, has file shares on my LAN, and just in general is a neat piece of equiptment. Plus it's full size AT which is my favorite style of case for old stuff. Also has a SoundBlaster 16, Zip Drive, SVGA 1MB Graphics Card, and I'm still, after 6 years of ownership, am trying to fill the massive 540MB hard disk with 286 era software till it can't hold no more (LOL)!
- The Franken-Business-Machines industrial Anti-Portable PC (aka, IBM Industrial/Portable PC in a Clone Chassis) - A Terry Yager provided true blue IBM system board, mounted in a SongCheer XT chassis with a 150 Watt PSU, various mods made to the board with a soldering iron (Reset, Power LED), XT-IDE controller with 2 IDE HDD's on it (and maybe later take one out and add an SDCARD Reader), 9-pin and 15-pin graphics via a 1MB ATI All-In-Wonder card with proprietary Microsoft Mouse port. I'm still thinking of robbing one of the 360K drives out of the Tandy and putting that in it instead of the 1.44M floppies, and then putting my SCSI MO-Drive beneath the floppy (giving me a spot to put the 500MB SCSI HDD in the Tandy).
. . . about your 'hot-rodded' 486 - have you ever attempted WIN98/2000/Xp? Just curious.