I bought a cheap pre-built in January of 2010 and have slowly upgraded it since then. It plays almost everything I want to play well enough still.
I'm thinking of building an entirely new system (with only one or two parts carried over, e.g. my SSD) to play Watch_Dogs, GTA V, Star Citizen and The Witcher 3 in all their glory. So, between late this year to mid next year, looks to be when I'll consider upgrading.
CASE: RAIDMAX Tornado ATX-238WU (Blue/Black) It's cheap, but also flimsy.
PSU: 550W ePower An off brand PSU that hasn't caught fire or exploded; I must be lucky?
MoBo: ASUS M4A78 PLUS Sometimes I wish it had SATA3 and USB 3, but it's good for a budget MoBo
OS: Windows 7 Pro 64-bit It operates my system
ODD: LG SuperDrive DVD/CD Watching movies in little box next to a game in windowed mode, is something I've done way more than I ever thought I would. What a stupid habit... I barely pay attention to the movie/TV show or sometimes the game
Storage: 1TB WD HDD, 500GB WD HDD, 128GB Crucial M4 SSD, 250GB Seagate external
CPU: AMD Phenom II x4 970 BE @ 3.5GHz A decent budget CPU. It can't handle modern MMOs like TERA or Guild Wars 2 worth a hoot, but it's sufficient for most everything else
RAM: 8GB Kingston Hyper X DDR2 @ 866MHz Not sure what possessed me to upgrade from 4 to 8 GB, but I did. Silly me. I haven't even noticed a performance difference xD (other than Sony Movie Studio running much worse than it used to, lol
GPU: XFX Radeon 6950 2GB This is equivalent on the Nvidia side to a 560ti. It's good enough, I guess. Wish The Witcher 2 ran a little bit better, but everything else is fine
Mouse: Logitech G500 Found one for $35; I think it was worth it. The precision and weight is much nicer than on a cheap-o mouse. Being able to control music/podcast from any program is nice. Having my PTT key for Ventrilo on my mouse is irreplaceable. So nice.
Keyboard: A cheap Logitech one that I got for free with something I bought at some point. Has a button that brings up the calculator program! Bling, bling, and such.
Headphones: Razer Carcharias. Well... they're a mixed bag. The mic is and always was terrible (thankfully I don't use it anymore). They leak sound like nothing else I've owned. Before I switched to a table mic, I got frequent complaints about broadcasting game sounds over Vent. However, they sound nice enough (they're several years old and thus have been well "broken in," I think they sound better than several $200 cans I was demoing the other day /shrug) and their biggest plus: They are the most comfortable headphones I've ever had. Every single pair of headphones I've ever owned, including ones in the same over-the-ear style as the Carcharias, have hurt my ears at some point. I've worn these all day many times, and they've never so much as produced a dull aching in my ears. Worst is my ears get slightly warm in Summertime. Very comfy cans.[/i]