I had a few things to consider, and they didn't all work together well. At all. First, I wanted something energy efficient, in order to soothe my bleeding heart, and hopefully not destroy my electricity bill either. I'd also have preferred to have parts not made from blood cadmium or whichever, but that's unfortunately far too difficult to research. On the other hand, I wanted power - enough to play new games for three years or so. Happily, the rate of technology has slowed down over the last decade, so this is actually pretty possible to do. More good news - newer technology in chips and in video cards indicates that they're actually better than previous models at lower power usage, even when they're more powerful overall, because they do a better job of lowering energy using when not being used at full force.
Of course, the bigger issue is money. I didn't get that big of a tax return. Unfortunately, since the newest of those more-efficient pieces of hardware had the best efficiency, I'd have to figure out how much money to spend on bleeding-edge stuff now, which is "not very much." I also wanted to avoid doing too much computer-building, since that can be a pain in the ass, but I left it as an option.
I'm happy that I did keep that option open, because I cut probably 20% of the cost out, and was able to research my parts directly. Here are my specs:
Operating System: Windows 7 Home Premium 64-bit*cannibalized from older computer
Motherboard: MSI MS-7642
Processor: AMD Phenom(tm) II X4 955 Processor (4 CPUs), ~3.2GHz
Memory: 4096MB RAM
Video Card: ATI Radeon HD 5670
Video Card Display Memory: 2295 MB
Video Card Dedicated Memory: 503 MB
Sound Card: Creative SB Audigy 2 ZS*
Total Space: 476.8 GB
Hard Drive Model: WDC WD5002AALX-00J37A0 ATA Device
CD-ROM Model: _NEC DVD_RW ND-3550A ATA Device*
All this was roughly $600. (though I also picked up Windows 7 and some accessories). No new monitor, though, and my current one maxes out at 1240x1040, so I'm not getting the very best resolution. But everything seems to be running well, Shogun 2 is a blast (my AV Club review is coming soon). I hope that this allows me to get more directly into reviews and discussions of current-generation PC games - and lets me play the best mods for the ones which have been out for a while.