If he hasn't purchased monitors yet and is focused on gaming, here's what I'd do:
Core components: $559
The Gigabyte is a high quality motherboard that can fit up to 3 video cards. The i5-3570k provides as much oomph as an i7-3770k for pure gaming, as gaming doesn't use hyperthreading. Consider the i7 instead only if video encoding is a core goal (live streaming being the most likely reason this is so). The cooler is the best & quietest air cooler. The RAM is... enough RAM. No reason for more.
Supporting components: $610
The case goes for the professional, understated look. It's among the 'sound-dampening' class, but you can also open up vents and add more fans if you want the 'air-tunnel' class performance option. Feel free to replace with something you think looks better, but this is an excellent case. PSU: Enough power for even 3 GPUs, will easily run 2 GPUs, even if everything is heavily overclocked. A very large SSD lets you put all your programs & games & os on the SSD for super-fast loading times. A large green hard drive for media storage, the green model because slow doesn't matter for media files and its quieter. A dvd-burner, feel free to replace with blu ray drive for more $.
Video Card: $780 or $820
2 Asus 7970s or EVGA 670s. The 7970s are a tad cheaper and have more video RAM in the case of very large resolutions. The 670s have a little more processing power, but less video RAM and are a bit more expensive. See monitor section for how to decide:
http://www.ncix.com/products/?sku=71941&vpn=02G%2DP4%2D2678%2DKR&manufacture=Others&promoid=1067Tower total: $1949 with the 7970s, $1989 with the 670s
Not included: monitors, peripherals, windows, shipping, possibly taxes (not sure when the ncix website calculates that). Note also that NCIX and all the major computer retailers in Canada price-match with each other. So you can probably reduce the total with a bit of work checking other stores for prices on the same components and price matching when you find a cheaper version of the same product. Any extra money left in the build should put be put into peripherals or monitors.
Now: monitors. For high-end systems there are a variety of options, and luckily you're not already tied to a monitor. The main ones are as below:
1) Gaming on a single 1920x1080 or 1920x1200 monitor, usually a high quality (usually IPS) monitor like a Dell u2412hm, u2312hm, BenQ GW2450HM, Asus ProArt PA238Q, or Asus VS229H-P.
2) Gaming on a single 120hz 1920x1080 monitor. 120hz ups the maximum fps from 60 to 120, or allows 3D @ 60hz. Example: Samsung S23A750D, BenQ XL2420
3) Gaming on a single 27" 2560x1440 IPS monitor. The cheapest of the big monitor options if you get a Yamasaki Catleap or Achevia Shimian (see the display forum here for details). These are generally available only through ebay or similar servies.
4) Gaming on a single 30" 2560x1600 monitor. The biggest size consumer monitor, these things cost over a grand each. Example: hp zr30w.
5) Gaming on 3 of options 1,2, or 3. Costing anywhere form $600-1300, this option allows for stunning 5760x1080 or even 7680x1440 resolutions. But it's expensive, and requires some technical expertise.
Note that for any of the single monitor options, it is easy and painless to add a secondary monitor that is not used for gaming, but for displaying normal desktop tasks. As for what video cards to use - the 7970s will be better for multi-monitor gaming. Also, cheaper to add a third if you're so inclined. The 670s will be better for single-monitor gaming, although 2 of them are very overkill for option 1. In some cases, the 7970s might be better on the 2560xXXXX resolutions if you play games with lots of VRAM-hogging mods or settings. If money is no object you can replace the 670s with 680s (the same caveats about better for single-monitor & worse for multi-monitor apply), but in general the drop in price from top-of-the-line to second-to-top is very large compared to a very very small drop in performance.
Edit: You can see xRehab and I put together pretty similar builds, though for a variety of small reasons I like mine better. Also, Canadian retailers
.Edited by MisterFred - 8/4/12 at 12:51pm