Thanks! I'll wait for more replies though before I make a decision. Also, I'm not buying the parts right now but I figured that it'd make more sense to be organized instead of rushing for parts when the time comes. If the hardware is truly better by then though...
Technology marches on such that every few months, the same money will get you better bang for your buck. No way around it, can't stop progress.
Gimlet is correct that the case is less time sensitive than the other parts. You may also be able to buy a data-only HDD ahead of time without losing much to progress.
Making a list like Tellemurius did and updating it once a month to account for the passage of time is a good exercise. In parallel to that, also read up on the technology of the parts, to better understand what caveats may come along (performance, compatibility, etc), and how to choose parts to mitigate those caveats.
Examples:
There are limits to how much RAM you can have, depending on your operating system and hardware. In Tellemurius' List, he picked 16 GB of RAM, but did not list an operating system... Windows 7 you would need at least Home Premium to use all 16 GB or RAM, Win7 Home Basic caps out at 8 GB, and Win7 Professional/Ultimate/Enterprise all have a much higher ceiling of 192 GB. (meant for servers and workstations, but uber-RAM in a gaming box could have benefits)
The power supply unit needed is based on the motherboard's needs, and the video card's needs. You should chase down the online manual and find out what those numbers are ahead of time. The PSU should be of wattage at least as high as the larger of those numbers, probably more like add them together, and maybe add another 10% or 20%. If the PSU gets tired as time goes on, you'll have some head room as its efficiency dwindles.