Here's my single vendor entry:
http://pcpartpicker.com/p/CBhZvK
This build turned out remarkably similar to my current PC build. PC Part Picker didn't have the Amazon price listing for the OS, so I manually searched for it and entered the price. If you prefer to go with Windows 7, the price is similar. Monitor, keyboard and mouse are taking a fairly substantial chunk of the budget, so if you wanted to go cheaper on those, you could go with a larger SSD or different video card but since it's a gaming machine I think the presentation and interaction is important as well. Could go cheaper on the case as well, but this is the case I'm currently using and I'm pretty happy with it. Easy to work in, good airflow/cooling options and extraordinarily quiet.
Processor is the
Core i5-4690K. Unlocked multiplier for overclocking. If you're not interested in overclocking, then the Core i5-4690 is a few dollars cheaper. There's literally $5 difference in the price on Amazon, so I see little reason not to get the unlocked version. Going with an i7 isn't necessary and generally counterproductive for gaming since few games support hyperthreading.
Motherboard supports 32gb of memory and SLI/crossfire so there's room for expansion later. This is the motherboard I'm currently using (with an i7-4790) with a similar memory configuration. BIOS was easy to navigate and set up. The more gaming oriented motherboards will have more/better options for overclocking/SLI etc but will increase the price.
The optical drive was literally the cheapest I could find. The only thing that you'll likely be using this for is installing the OS. If you have an 8gb flash drive, you could install from USB instead.
Video card: The GTX 970 runs Arena Commander smoothly at the native resolution of the monitor (1920x1200) on high. I've also had no issues with everything else I've thrown at my GTX 970. The 970 has ridiculously low power draw compared to previous generations of cards, you should have no issues going with a lower wattage power supply than the one chosen. The PSU was purchased with a much different video card setup in mind (Dual Radeon R9 280x).
Full disclosure: I don't work for Corsair and they're not giving me any money, I just happen to like their products. However, I do work for Dell.