Okay, unless there's price changes or special deals anytime soon, I think these are what I'm going to get:

Power Supply: Antec 750w Current High Gamer series 100 USD
http://www.newegg.com/Product/Product.aspx?Item=N82E16817371049

CPU: Intel i5-2500k 230USD

Video Card: HIS IceQ Radeon HD 6950 2GB 270 USD
http://www.newegg.com/Product/Product.aspx?Item=N82E16814161372

Monitor: Asus 23" LED IPS 190 USD
http://www.newegg.com/Product/Product.aspx?Item=N82E16824236122

Memory: Kingston 2x4GB DDR3 40 USD

Keyboard: Logitech Wireless Combo 26 USD
http://www.newegg.com/Product/Product.aspx?Item=N82E16823126197&SortField=0&SummaryType=0&PageSize=10&SelectedRating=-1&VideoOnlyMark=False&IsFeedbackTab=true#scrollFullInfo

That's about $850 so far. I still need to pick out a motherboard, a hard drive, and a case.
What's a good price for a motherboard or hard drive to go with this? And what kind of hard drive should I get?

The best motherboards for the "Sandy Bridge" CPUs use the "Z68" chipset, but most are expensive. The "P67" chipset is a good second choice. Other chipsets are inferior to these two.

I have this one, which has features comparable to many more expensive motherboards and is a very good deal once you cash in the rebate:
MSI P67A-GD45
http://www.newegg.com/Product/Product.aspx?Item=N82E16813130582
$110 after rebate

For a Z68 motherboard, this is deservedly popular, but I still like the MSI board above better:
ASRock Z68 Extreme3 Gen3
http://www.newegg.com/Product/Product.aspx?Item=N82E16813157271
$122 (no rebate)

Remember the floods in Thailand back in November? A lot of hard disk production ended up underwater, and the market has not fully recovered. Prices are twice or more what they were before the floods, and many popular drives are still scarce.

The best consumer hard drives are the Western Digital "Caviar Black" series. This one costs too much, but it's a better deal than many others, and good enough for any single-drive setup:
Western Digital Caviar Black 1TB
http://www.newegg.com/Product/Product.aspx?Item=N82E16822136284
$180 (no rebate)

Okay, thanks. It's so weird how weather on the other side of the planet can affect a niche computer market. I think that's really cool. Except for Bangkok being under water.

That HD looks good, but I doubt I need a Terabyte of storage. I never take pictures or videos, so I probably wont use it for anything but games. Does it have to be an internal hard drive, or would an external one work with games?
What is the cache rate on the hard drive? Do I need to take that into account?

External drives have a much lower transfer rate than internal drives, which will give you a massive performance hit when games try to perform time-sensitive read/write operations. Basically external drives are for storage, internal drives are for running programs.

I may bemissing something, but where does an internet connection fit into all this? Which one of these components will allow me to connect to my wifi?

If you have a wired connection to your gateway, the Ethernet port on the motherboard takes care of it.

If you prefer (or must) use a wireless connection, a USB WiFi device will do that for you. I have used and like both of these:

Zonet ZEW2590
http://www.newegg.com/Product/Product.aspx?Item=N82E16833130078
$20

Zonet ZEW2540P
http://www.newegg.com/Product/Product.aspx?Item=N82E16833130068
$24
This one connects via a USB cable; this makes it a little more flexible in where you can place it.

You'd be surprised how fast you use up disk storage. A terabyte is not too much nowadays. And that particular disk drive is a better deal than many of lesser capacity. As for cache, the bigger the better, but "Caviar Black" drives are premium drives and usually have the largest and fastest cache available.

Windows 7 fully patched can be over 20GB, Mass effect 3 is 15GB, SWTOR is over 28GB, skyrim fully modded is upto 20GB... spending money on the largest drive you can afford is usually a good idea though if your careful you could get a small drive now and wait for prices to drop though you likely would still end up spending more than getting a large drive now
If you can go wired go wired especially if you plan to play online at a competative level Wifi adds to latency...
My gaming PC's are wired my work PC is wireless ;)

I think I've got a good hard drive and motherboard picked out. What about cases? I was thinking this one looked good:

http://www.newegg.com/Product/Product.aspx?Item=N82E16811129066

Good case. It's been around for a long time and gets the job done. Plenty of room for a big graphics card and a big CPU cooler. Antec cases are substantial and heavy, which is a Good Thing.

I detest blue lights, and so does my dog, but that's just us :)

Great! I think I've got most of the components picked out. I'm hoping that by April or May the Hard Drive and video card will be a bit cheaper.

Do I need to buy windows 7 separately? I didn't see it included with anything. On a related note, I have a cd copy of system shock 2 laying around, and I'd really like to play through it again. I heard window 7 Ultimate has an xp emulator so you can do just that. Is it worth paying extra for?

Oh, I forgot about Disk Drives. Does it matter what kind I get, as long as its CD/DVD? I mean, PC disks arent going Bluray like PS3 anytime soon, are they?

Yes it's a seperate purchase, OEM's are cheaper but locked to your MB Retail can be moved to new MB's. In all honesty Ultimate isn't really worth it for xp mode just get a virtual machine if you must remember to be sure you get the x64 version

Yeah, you also need an optical disk drive. They are not expensive, and they are sort of expendable, because they will eventually burn out if you use them to burn a lot of disks.

I favor Toshiba/Samsung. I particularly do not like LG, which has really annoying driver update crapware. YMMV.

Wodmarach gave you good advice about Windows. The "OEM" version is a lot less expensive, but it will be locked to your motherboard when you activate it. Sometimes you can work or beg your way around that lock, but in general figure that an OEM copy stays with that motherboard.

The "Home Premium" version is good enough for any home or home-office use. And do get the 64-bit version. The only reason anybody would want the 32-bit version anymore is for really old setups with a 32-bit CPU or hardware that doesn't have new signed drivers.

So I don't want the OEM version? Cause the normal version is almost $200.

depends on if you intend to upgrade your MB in the next 3-4 years tbh by then we'll likely be on windows 9 and time to upgrade your OS again...

I'm not really planning on upgrading a motherboard anytime soon. I might add another card in a few years though.

I think that's everything then. Here's what I've got picked out:

Power Supply: Antec 750w Current High Gamer series 100 USD
http://www.newegg.com/Product/Product.aspx?Item=N82E16817371049

CPU: Intel i5-2500k 230USD

Video Card: HIS IceQ Radeon HD 6950 2GB 270 USD
http://www.newegg.com/Product/Product.aspx?Item=N82E16814161372

Monitor: Asus 23" LED IPS 190 USD
http://www.newegg.com/Product/Product.aspx?Item=N82E16824236122

Memory: Kingston 2x4GB DDR3 40 USD

Keyboard: Logitech Wireless Combo 26 USD
http://www.newegg.com/Product/Product.aspx?Item=N82E16823126197&SortField=0&SummaryType=0&PageSize=10&SelectedRating=-1&VideoOnlyMark=False&IsFeedbackTab=true#scrollFullInfo

Motherboard: MSI P67A-G45
http://www.newegg.com/Product/Product.aspx?Item=N82E16813130582

Hard Drive: Western Digital Caviar Black 750GB
http://www.newegg.com/Product/Product.aspx?Item=N82E16822136794

Case: Antec 300 Illusion
http://www.newegg.com/Product/Product.aspx?Item=N82E16811129066

A Samsung disk drive
http://www.newegg.com/Product/Product.aspx?Item=N82E16827151250

And Windows 7 Home Premium OEM

Right now that's about $1300. Hopefully in the next few months some of the prices will go down.