I use a quite old computer, fully satisfying me.
It has:
Motherboard: Gigabyte GA something, xD don't remember, North bridge is P35, south bridge is ICH9
CPU: Core Quad Q6600 @2.4GHz
RAM: 8GB DDR2-800
Graphics card: Nvidia GeForce 8600 GT
HDD: 250 GB WD
SSD: 32GB Transcend
SSD: 60GB Patriot
Monitor: 19'' Samsung SyncMaster 940nw
Also I have 21'' Philips monitor with an HDMI port bought specially for work with arm/mips SBCs.
OSes: Windows XP SP3 (the same installation from the start in 2008), Windows XP x64, Windows 7 x64.
I also have a spare desktop with Core Duo E8400, and AsRock motheboard (G35/ICH7), 320GB and 160GB WD HDD, it lacks memory.
And a laptop from 2012 year, Core i3-2330M, 4GB DDR3, 640GB WD HDD, Windows 10.
Aaaand - iMac g5
with some PPC CPU inside, forgot the model, it is from 2004 and has only 512MB of DDR, no PCIe, some AGP graphics card, quite lagging behind its PC counterparts from the same time, but, of course being more expensive, it's apple, everybody. I've bought it just for fun. was dreaming somewhen to play with the PPC architecture.
And of course, I have a small bunch of arm/mips SBCs as targets for my hobby.
I guess I mentioned them here already. Shortly, it's Beagle Bone Black, Cubieboard 2, Pine64+ 2GB, CSA90 set top box with octacore rockchip rk3368 SoC, Banana Pi M2 Ultra and Mips Creator CI20.