I agree with waiting, but in the meantime "build" a PC on paper, then read reviews for each part to figure out the things you should be looking for.
There are some basic points to be aware of:
1) A modern $200 CPU has enough processing power for about TWO high-end single-GPU graphics cards. Don't go crazy on an expensive CPU. I'd spend no more than $300.
2) The noise and cooling solution on a graphics card is very important.
3) Decide if NVidia has solutions like PhysX or CUDA which you desire. If I was buying today it might be a GTX 560Ti.
4) a quality power supply is VERY important. Spend some time reading about that. Antec and Corsair are two good names. There are others.
5) Computer cases really vary. Personally I'd just get the Antec 300.
6) I recommend either 4GB or 8GB of RAM, no more. The 8GB only provides a very small benefit over 4GB in multi-tasking. The only game benefit may be a reduced initial loading time.
7) SSD. It's worth it. I recommend a 120GB OCZ Vertex 2. The Vertex 3 is 2x faster but more expensive. Personally I don't think it's worth it.
8) HDD. I recommend a 1TB of 2TB Western Digital. Either Green or Black. If you get an SSD you'll want to install your games to your hard drive by manually choosing the startup folder. I have this setup for Steam and non-Steam games. Steam only requires that you initially designate the folder once and it's all automatic after that.
"E:\Games...", and
"E:\Steam..."
9) Which version of Windows? There's almost no debate:
"Windows 7 Premium 64-bit OEM"
*If you have a Western Digital hard drive installed you can use their free version of Acronis True Image to make backups of your C-Drive. I STRONLY urge you to do so after you initially install and Activate Windows, then later on again with updates etc installed. Make periodic images.