My first real GPU was an ATI Mach8, advertised as an 8514/A clone that would actually fit into an ISA slot instead of requiring a micro channel system, which made it about $10.000 cheaper than the 8514/A equipped PS/2 original. It required a VGA to go with it and that was probably some Tseng Labs based card, of which I had many generations, too.
It was the first true graphics accelerator I owned, it would accept high-level commands to draw lines and rectangles etc., instead of being a bit-mapped frame buffer, which all suffered from a crazy slow memory interface across an 16-Bit 8-MHz ISA bus: things could get animated!
First frame buffer style graphics card I owned was an EGA, first graphics card I used and programmed for was a Hercules monochrome graphics card on the IBM PC-XT.
I never owned a slotted CPU, it was always sockets right from the first 6502 and Z-80.
But the first slotted video card would have been a Videx-2 80-column card for an Apple ][.
No idea on the host for the Mach8, after a single 80286 there were so many iterations of 386, 486 and then KII and KIII, I've lost track. And yeah, there was a Pentium Overdrive 83 somewhere in there, too.
Had quite a few ATI cards after that, I don't think I left out any generation but the last (discrete) was an R9 290X.
Nvidia came late (there was a Vodoo3D, but that doesn't count), first was probably an 8800 GTX. I only distinctly remember it was a chip etched in 90nm and had GDDR RAM of some type.
I had one ATI/AMD and one Intel/Nvidia system for a couple generations, and went with team green once I got into CUDA and ML.
For completeness: I got a NUC with an ARC770m, mostly because it was the same price as a NUC without the ARC.
I also used to own a TMS34020 EISA based dGPU capable of 1080p and 32-bit true color and ported X11R4 to it as part of my CS thesis. To my knowledge it was the first true color X11 port while Thomas Roell was working on some of the more popular (and much cheaper) 8-bit color cards for PCs.
Perhaps also interesting:
The first system I owned was an Apple ][ clone that was fairly complete with Z-80, 80-column card, dual 140k floppy drives and a monochrome TV style monitor which was around $2000 in 1983. It was really the cheapest and most versatile CP/M system around as well as a "gaming computer" (the Apple personality of that hybrid) for after-hours.
The upgradability offered via slots was key, it would eventually have a Z-80B card with 3x the performance of the original SoftCard as well as a giant 1MB floppy drive, which felt pretty near a Winchester drive at the time (those started at 5MB).
My Apples never had color because I live in Europe where NTSC TVs didn't exist: we had PAL, which was so much better, but incompatible. Monochrome made me sick and desperate.
I was free-lancing as a programmer while studying computer science and PCs were the "professional choice" for the tenders. So I went full out with a 80286 based system finally including mind boggling color (16 out of 64) with a 640x350 non-square pixel EGA, which was acceptable for text (CGA was too painful), but also offered bit mapped graphics.
That initial system had a 8 MHz 80286 IBM PC-AT clone, 1MB of parity RAM, 20 MB 5 1/4 half height stepper motor MFM HDD, 1x 1.2 MB 5-1/4 floppy disk, EGA graphics, parallel and serial ports and a NEC P5 4 color dot matrix printer and did cost around $10.000 in 1986.
It was the price of a new VW Golf or a used Porsche, but I saw no way to make money driving cars.