Craigslist is my new friend for lightly used computer components.
I just got a new computer that is finally able to play Crisis on medium settings. Total grass-roots too: Pentium Core2 Duo, 2gigs RAM, GeForce 8600GT, 250gig hard drive. Not too fancy by today's standards. But I got it all for $240! (I bought a brand new Antec TruPower Trio PSU for $40 from another guy.) All I needed was to slap it in a case with optical drives that I had sitting around.
Double GRM rig, since the guy I bought it from is not only a fellow GRM reader, but a LeMons competitor. Best experience I've ever had buying on Craigslist. He helped me troubleshoot the machine when there was a minor hardware conflict. GRM folks are great.