Alright, my specs it is...
Case - Cooler Master Centurion 590
Cooling - 6 Thermaltake TT-1225s. That's 6 high-powered fans with blue LEDs. Excessive cooling, but not as loud or as bright as you'd think.
CPU - AMD Phenom 9550. Quad Core, 2.2 Ghz, 95 Watts at full throttle (which I don't think it ever has been)
Motherboard - Asus M3N78 Pro. Onboard video is an Nvidia 8300, almost enough power to play Portal.
Video - XFX Nvidia 8800 GT.
Hard Drive - A lonely 250 GB Seagate Barracuda.
DVD - Pioneer (random numbers and letters go here) that'll take damn near any disc you can throw at it short of Blu-ray.
Power - 550 Watt Ultra X-connect 2
Operating system - Windows XP SP3
Memory - 2 GB Kingston Twinx DDR2
...and sound - A comically out-of-date Sound Blaster Live! (yes, with exclamation point) 5.1 channel surround sound card.
So, you seek advice?
Graphically, I wouldn't recommend any less than the 8800 GT. They run around $100 US and will handle damn near anything you throw at them. Nvidia has been good to me, ATI has not, although I'm sure others here will say the opposite.
Any motherboard the handles quad core processors will take dual cores as well, so spend money here. If money is tight, get a dual core now and upgrade later when that power can actually be used. Intel is the performance leader in CPU-land, AMD the price leader. A quad core like mine runs about $150 US, and I have yet to tap all of it's power yet. AMD fan that I am, any dual or quad from either company will serve you well.
(Yes, I realize I called myself and AMD fan, and yet I'm not a fan of ATI. Deal with it.)
Memory seems to be dirt cheap these days, so max that out. If you still run XP, 3 GB is about the limit. If you run Vista (or plan to run it), go nuts, you will not be able to buy enough to max the OS' limit.
The rest is pretty much minutiae. As for you AGP users out there, [a href=http://www.newegg.com/Product/Product.aspx?Item=N82E16814129116]you're not done for yet.[/a]