Dual 1.25 G4 MDD, 1GB of RAM, 80GB HDD, original Radeon 9000 Pro 64MB running 10.5.8. Was my main machine for the bulk of 2010, actually... only to be usurped by my own custom-built PC when I finally got a decent enough processor in it. (The original build cost me literally nothing though, since I was given the parts as part of a program... so ultimately a great deal.) Said PC runs XP and Ubuntu - 7's just been an absolute nightmare for me.
I've been thinking of setting up a Dual 1.8ghz 2004 G5 I recently saved from the trash room at my college for $1, though. I had to replace the battery and add an optical drive to it, but it wasn't a bad project at all. Came with 2GB of RAM (which I figured I'd slap into the G4 if the system didn't work... still worth the dollar), Radeon 9600 XT 128MB (again, could try it in the G4 if it hadn't worked), and 160GB HD. Wanting to flash and add a 7800GS, but the price is just way too high to justify a marginal upgrade (even if I could swap the G4's card...).
I so badly want an iMac G3, but I just don't have a place to put it, nor would I be able to justify it being really useful (so my mother would likely end up whining incessantly about it).