Heres mine
CPU: Intel Core I7 920 @ 2.67Ghz
GPU: 1GB Asus HD 5850
MoBo: Gigabyte EX58-UD3R
RAM: Kingston 4Gb Dual-Channel DDR3 @1333
HDD: 1Tb Seagate
PSU: 430w came with case
Case: Thermaltake M9
OS: Windows 7 premium 32bit Trial(cracked)
LCD: Benq G2420HD @1920x1080

Tower:
CPU: Athlon II X2 250 (3 GHz)
RAM: 8 GB Crucial DDR3
PSU: Tagan TG480-U15 PSU (480W, I guess)
MoBo: Asus M4A785T-M
Case: CoolerMaster CM 690
Graphics: Sapphire Radeon 9750, 1GB RAM
Screens: Two LG Flatron L2000CN (20") at 1600x1200 each - giving a total of 3840000 pixels to play with
HDD1: 700GB SATA (100GB system+apps, 120GB games, 30GB docs, 450GB stuff-that-don't-fit-elsewhere-because-the-drives-are-full)
HDD2: 300GB SATA (music)
HDD3: 300GB SATA (video)
HDD4: 300GB SATA ("trials", "demos")
HDD5: 235GB PATA (unsorted downloads)
Optical: TDK DVD writer
OS: Windows 7 Ultimate x64
Laptop:
CPU: Core2 Duo P8700 (2.53GHz)
RAM: 2GB of something
PSU: uhh... Lenovo 90W
MoBo: Lenovo Thinkpad R500
Case: see above
Graphics: Radeon HD3400... series?... with 128 MB RAM
Screen: 15,6", 1680x1050px
HDD: 300GB SATA
Optical: Matshita DVD writer
OS: Windows 7 Ultimate x64
Mac Mini:
CPU: 1,83 GHz Core2 Duo
RAM: 1GB DDR2
PSU: Apple 110W
Case/Mobo: It's a freaking Mac Mini, can't be that many variations, can there?
Graphics: Intel crappage, probably a 950G or whatever they're called
Screen: LG Flatron L1752TQ
HDD1: 80GB SATA
Optical: DVD writer taken from an earlier Mac Mini because this one only had a DVD-reader/CD-writer.
OS: Mac OS X Snow Leopard (10.6)
Server:
CPU: 1,25 GHz PowerPC G4
RAM: 1GB DDR
PSU: Apple 90W
Case/Mobo: Earlier version of the above machine
Graphics: ATI something, 32MB
Screen: shares one screen with "Tower", dual inputs is a good thing
HDD1: 120GB PATA (the original 40GB one decided to die somewhere along the ride)
Optical: The CD-writer/DVD-reader from the above machine
OS: Mac OS X Leopard Server (10.5)
Pizzabox:
CPU: MC68LC040 25MHz
RAM: 36MB (4MB soldered onto the Mobo, 32 in the only slot)
PSU: Dunno, wouldn't want to try finding a new one if it broke
Case/Mobo: It's a Macintosh Performa 475, look it up
Graphics: 256kB VRAM (upgradeable to 512 kB by adding another stick which I don't have)
Screen: sadly, the original 13" screen has long since been discarded, now hares screen with the next machine
HDD1: 4GB SCSI2 (originally 150MB, later 250MB)
Optical: External SCSI 4X CD-ROM drive
OS: Mac OS 8.1 (originally System 7.1, disks now long lost)
Second Performa:
CPU: PowerPC 601 75MHz
PSU: Ditto the above
Case/Mobo: Look up the Macintosh Performa 6200
Graphics: no idea
Screen: Some 15" Apple CRT with the slightly weird max res of 832x624
HDD1: 2GB PATA
Optical: SCSI CD-ROM
OS: Mac OS 9.1 (originally System 7.5)
Old laptop: (no longer in working condition)
CPU: Pentium 3, I forgot the speed
RAM: I think I put in 256 MB
Graphics: SIS 4MB, I think
HDD: No idea
Screen: 1400x1050, 14 or 15 inch
And then there's the 386 laptop, the 486 (or was it Pentium?) laptop, and a couple husks of old towers.

CPU: AMD Athlon II X4 620 (2.6ghz Quad Core)
RAM: 4gb DDR3 (1333mhz I think)
GPU: ATi Radeon 4850
HDD: 250gb SATA
Mainly runs Gentoo Linux.
And it has a 22" 1680x1050 monitor, and a 17" 1280x1024 monitor.

bit small don't you think?

Yeah, probably. One can never have too much space for porn these days.

Macbook Pro 15-inch with 2.53 ghz Core 2 duo, 4 gb RAM, and Nvidia 9400.
Using bootcamp with a 55 gig partition of Windows XP for all my GOG games.

It always amuses me when I read threads like this where people talk about "old" computers with 2Ghz Processor and at least 1GB RAM :-) I have (and was my main computer up to about a a year ago) an old eMachines with Windows ME:
733Mhz Processor
512MB RAM
18GB HD
and I don't even know what kinda video card! :-)
That's enough (most of the time) to run Homeworld 1 and Cataclysm, NFS Porsche Unleashed, and any old DOS game you've got! ;-) Now I've actually got another computer at the moment that has 1.8Ghz, 700MB RAM.
But my "real" computer rig I'm about to get in a few days (hopefully). It's got 2.4Ghz processor, 4GB RAM, 320GB HD and a Nvidia G100 (I know, not the best computer ever...but it's under $100!!)

Processor: Intel Core 2 Duo E6750 2.66GHz, 1333MHz FSB, 4Mt Cache, S775
GPU: Sapphire Radeon X1950 Pro Ultimate, PCI-E, 256Mt
Display: Samsung SyncMaster 204B 20" TFT (1600*1200, 5ms, HAS+PIVOT, TCO03)
RAM: 2 * 1Gt 800MHz DDR2 Non-ECC CL5 Dimm
PSU: Zalman 500W PSU with Heat Pipes
Motherboard: ABIT IP35 ATX
HDD: Samsung T166, 500Gt:n SATA2, 7200RPM, 16MB Cache
Case: Antec P182B
OS: Windows XP Professional SP3

I'm curious, was it good for anything? I considered it at one point but would have had to order it from the US at the time. Shame they seem to have scrapped XO-2.

OS : Windows Vista Home Premium 32 Bit
Processor : Intel Core 2 Duo E8400 3 GHz, 1333 MHz FSB
MB : Gigabyte EP35-DS3R
Graphics Card : NVidia GeForce 8800GTS 512
Monitor : Dell E228WFP 22" WS
Memory : 4 GB 1066 MHz DDR 2
PSU : Coolermaster 750W
Hard Drives : Seagate 500 GB, SimpleTech 640GB external
Optical Drive : Samsung SH-203B
Peripherals : MS Digital MEdia Pro Keyboard, Logitech G5 Laser Mouse, Logitech 160 Watt 5.1 Speaker setup

MB: Asus m4a78-em
CPU: AMD Phenom II x3 710 2.6 GHz + Scythe Ninja 2 cooler
RAM: 6GB Corsair XMS2 DDR2 800 MHz
GPU: XFX GTX260 896MB
HDD1: Samsung F3 1TB
HDD2: Seagate 320GB
HDD3: Seagate 640GB
DVD: Optiarc DVD-RW AD-7200S
PSU: Corsair VX550W
Case: Antec p180 Mini
Screen: Eizo s2001w 20" 1680x1050
Sound: Nuforce uDAC + Denon AH-D1001 headphones

I'm running a standard Macbook 2.26 GHZ with 4 GB of ram. I'm running a partition of 120 GB using Windows 7 Pro 64 Bit.

It's awesome to use outside in the sun during summer. When the backlight is switched off, the screen is in a grayscale e-paper mode. I can surf the web or even watch movies in bright sunlight. With the backlight on, (when I'm indoors) the screen is like a normal color LCD. I don't own a normal netbook, so it fills the "light and portable" role for me.
On the downside, the CPU is very slow. For example, you have no chance of watching flash videos on it. I've tried a couple of dosbox games, that seems to work well. It plays many types of video files, but not all (I have to avoid videos with high resolutions or any AVC/H.264 encoded files)
Rumor is that PixelQi (the company that makes the OLPC screens) will soon make their screens available for end users to retrofit in normal laptops. The dual mode screen combined with the processing power of a fully fledged laptop or netbook would be great.

Intel Core 2 Quad cpu Q6600 @2.4 ghz
4 gb dual channel ddr2 @399mhz 6-6-6-18
Windows 7 home edition 64 bit system
Hp w1907 wide screen lcd monitor
Nividia 9800 Gt 1028 mb
Motherboard: Pegatron corperation bencicia (cpu1)
Hardrive: 750GB segate st3750630as (sata)
audio: Xreative x-fi audio processor
I got mine in 2008

Fair enough, GoG is more then welcome to shut down this thread or lock it then. I would do it myself, but for the life of me don't know how to do it. But the threads are mildly different, his purpose for asking what hardware GOGers have was to help him with a purchase, mine is to see if the house of good old games is also the 'house' of good old hardware.
I never really did believe that and the results posted here pretty much validate that, there are some awesome hardware in use, and awesome laptops, like Jonhman's.
Brilliant result though, a nice mixture of the old and new, and a wicked range of brand names, as a brit, I never heard of mushkin before, or tagan.