Okay, I'll bite. Quite a few machines in active use right now, most of these were free-ish or cheap used or acquired in some non-monetary way. Ironically by *FAR* the most expensive system to me was the P233MMX build, I'm probably about $400 into that. (Yes, that includes the Macbook Pro which ended up becoming mine for around $200 thanks to a convoluted series of trades and a liquidating company.) So right now around the apartment I have:
Everyday / general purpose laptop: 2012 Macbook Pro - Core i5 @ 2.5 GHz, 4GB DDR3/500GB HDD, Intel HD 4000 graphics, OSX 10.8.4. No, I'm not going to upgrade to Maverics/Yosimite/El Capitan/whatever. Many, many tweaks to make it behave more like a Unix machine. Also has Unix machine problems (dependency hell, multiple versions, etc. - ask me about Python or Git or Java sometime) that most Macs don't.
Other laptop: HP Touchsmart TM2 (laptop w/swivel+foldable tablet screen & integrated Wacom stylus) - U7300 Core2 Duo @ 2GHz(??), 4GB/ 500GB, Intel GM45 GPU, (very outdated) OpenSUSE 11.4 (2.6 kernel) / KDE 4.4.
Retired laptop: Dell D430 - Centrino Duo @ 1.2 GHz, 2GB/120 GB, Intel GMA 3000, Linux Mint 13 (3.8 Kernel) KDE 4.12+XFCE+Awesome+Fluxbox, massive docking setup with a ton of expansions - sadly the LCD inverter went so I don't really use it anymore. Still works great with an external display though.
music recording workstation: PowerMac G5 2.3GHz DC (dual-core), 7.5GB DDR2, some HDDs (whatever I have left from the NAS build, probably 320 or 500 GB), GeForce 6600 256MB PCIe, will run OSX 10.5.x as soon as I set it up. Shares a really nice 19" Hansol CRT through a big KVM.
Music *sequencing* workstation: Advantech single-board industrial PC on massive 14-slot ISA backplane. P233MMX, 64MB 72-pin EDO, 20GB HDD, AWE64 w/28MB and GUS PnP w/8MB (yeah 2
ISA PnP soundcards in one rig - and they play *great* together, no config issues!), S3 Virge PCI 4MB + Voodoo2 PCI 8MB, 4U rack mount case, internal IDE ZIP & LS120 "floppy" drives, Adaptec PCI SCSI, too many other expansions to list. Boots FreeDOS 1.1 *only* with NO GUI or graphical shell whatsoever. Shares a really nice 19" Hansol CRT through a big KVM.
Other rackmount PC: dual P3/1000, Asus mobo, 1GB SDRAM, 2x160GB IDE, GeForce 4 TI4200 AGP, M-Audio 2496 sound card, Adaptec SCSI, network card, etc. Internal 3.5+5.25+IDE ZIP drives. Dual boots FreeDOS and AntiX 15/Fluxbox (a nice Debian variant.) Not sure what to use this one for now, was going to be the recording rig until I got the G5 towers. Shares a really nice 19" Hansol CRT through a big KVM.
Other G5 tower: 2.0GHz DP (two physical CPUs, one core each), 4GB DDR, 200GB laptop SATA drive, Radeon 9600 AGP, runs Debian 8 w/Cinnamon 2.4. Presently in my office doing worky stuff. (Sits next to my 8-core i7 workstation running Fedora 21 but that one isn't owned by me so it doesn't count. BTW I have 5 monitors in an arc on my desk, the Dell has 3 heads and the Mac has 2. I should get a picture.)
"Arcade cabinet" (build pics coming soon!) - P4 3.0 (800FSB), Gigabyte mobo, 2GB DDR/80GB HDD, C-Media 4-channel sound card, MS Sidewinder 3D Pro on DB15 gameport, Radeon 9600 128MB AGP using S-Video out to a massive CRT TV. Runs ~2005 era games and various 8/16-bit emulators really well. Not overly desperate to play anything newer (except modern indie platformers which generally run on my Macbook.)
"True vintage" stuff: 386DX/25 now running my EPROM burner, TI-99/4a with modern expansions, Yamaha CX5MII/128 MSX MIDI Computer with peripherals