With 2500 to spend you might as well get a decent case. By decent I mean quality aluminum stuff, not plastic fantastic shit. Look at Lian Li, they're one of my fav manufacturors of full tower cases (and cases in general, though Fractal Design offers some pretty good bang for the buck air cooling solutions)
Probably better off getting the V-Pro if you intend to OC and stuff. As someone who's had bad experience with Asus in the past (pre-sandy bridge, admittedly) I'll recommend you look at Gigabyte's mobos. So far I've only had good experiences with them and I intend to keep on using them myself. Alternatively Asrock makes great bang for the buck boards and doesn't really offer that much less performance with it's higher-end boards in comparrison to others. Hell, some people even hit pretty damn high clocks on their Asrock boards and laugh at others' precious Asus boards.
>2 GTX 670
Your call with the gfx cards, but a dual 670 setup is pretty much enough to rape any game you'll ever want to play. Should be enough for 3 screens, though I honestly recommend you don't. Most games have no to horrible tweaks to make them anywhere close to looking normal on a three screen setup and I can personally attest to that. In my opinion I would ditch the 3 screens in favour of two screens - a gaming 120Hz TN panel for single screen 3D gaming and a decent IPS panel screen for normal work.
Sounds reasonable but doesn't offer too much headroom for OCing your stuff if you ever get serious with the clocks / voltages. However if you're not a die-hard enthusiast, it should be more than enough.
Spot on, you better OC it or I'll find you and murder you for wasting your money
>OCZ Agility 3
Fuck OCZ, go with a Crucial m4 - best overall real-life performance and pretty much always at the top in specific categories
Stay away from Barracuda drives as if they were the bubonic plague. If you want a backup drive for your files/downloads/music etc. get a Hitachi or WD drive. Only two companies I still trust to make a quality cheap HDD, Barracudas have a history of dying, being useless and otherwise pissing off people that bough them.
>1600MHz CL10 Vengeance
Kinda bad for such a large budget, I would rather you get less ram but better. You want to find at least some 1600MHz CL8 stuff, which should allow you more space to adjust the timings and clocks to your liking.
Very meh about this one, but it might just be my view on things. Personally I have a "go all the way or don't go at all" view with LC. The H100 will perform worse than top-notch air cooling but at the same time it is quite affordable and easy to set up. I would honestly rather throw in another hundred bucks and get myself a proper LC kit that you can later expand to include the gfx cards and/or other stuff.
If you want "better" you can always just sacrifice stuff to get 3-way 680s or something, but imo the general idea behind your build is great. Looks like a nice overall performer with lots of space for future expansion, albeit perhaps not for the gfx cards (your only option would be to replace them or add another 670). From my suggestions I really recommend you switch the SSD and HDD, you'll save money and gain performance/reliability. Honestly the case and PSU don't matter that much, though I really think it would be a waste not to give such a build the look and power it deserves. Ram must almost certainly be switched if you want high-end stuff, and I personally recommend you go with a proper LC kit for two reasons: looks and performance. If you personally like a challenge I would recommend you sleeve all the cables too, just to give your PC those finishing touches you see in pro builds.