My dream machine, though I might not be able to afford it before Skyrim, is something like:
AMD's Bulldozer 8 core if it doesn't cost a ton. If it does, then one of the decent socket AM3 CPUs that can be replaced with Bulldozer or its successors down the line.
AM3+ motherboard for the above with onboard sound and hopefully USB 3.0
8GB DDR3 RAM (4GBx2) I always hear buying the higher frequency RAM is a waste of money, but what I get will depend on the current prices.
Hopefully a computer case that actually has USB 3.0 ports. Most current ones do not. I like fan air filters too.
Wireless N LAN card if it's not built into the motherboard
Graphics card is a big question mark now. Probably something along the lines of the nVidia 460/560 but if another mid/high card like those is great bang for the buck for 200ish dollars (no more than 250 if I can afford it). I'm unfamiliar with AMD cards right now but if it's better bang for the buck and cooler (temp wise) than nVidia I might get that.
64GB SSD if I can afford it and the prices go down some.
1TB HDD for standard documents and such. Maybe 2TB if they are cheap enough to not inflate the price much.
A very cheap (20ish dollar) DVD combo drive. I'll only get a Blu-ray if it's significantly less than 100 dollars. It's too easy to replace or add an optical drive for me to even think of buying Blu-ray at this point. I have a PS3 for that.
600-700W PSU... which is probably overkill but better a bit over than under.
I see things like mechanical keyboards as enormous wastes of money so I'd be using a 10-20 dollar five button mouse from Monoprice with an old keyboard.
I plan to use a copy of Windows 7 we already have that turned out to not perform well on an older computer.
If I can afford it, a 24" widescreen LCD monitor with integrated speakers. I'd use a USB headset most of the time anyway and I never found the need to spend much for sound.
I might wait until Cyber Monday even if I have the money at Skyrim launch. I'm not sure how much better those deals tend to be.
A machine like that will probably eat Skyrim for lunch. I'm guessing it would be considered a mid-high machine. Bulldozer will probably be more expensive than I'm hoping is why I say that. I think now would be a terrible time to put a machine together even if you prefer Intel. The fall or early Winter will be far more clear.