If you intend to go SLI Geforce 660Ti then a 750w unit would be more than enough as each GPU will only draw roughly 150-200w whilst gaming.
Plus when you add in a second GPU you don't automatically double the power used compared to just a single card.
Besides, there is a massive focus in the PC world with driving down power consumption, the CPU's and chipsets have made massive strides in this area over the last several years. Haswell will drive that point home even more so.

Mind you, this doesn't mean you can find the cheapest 750w PSU you can find and be done with, PSU's from the likes of Corsair, Seasonic, Enermax are all top stuff and generally would be good to stick with, but you do not need a 900w PSU, far from it, you need that for Triple/Quad GPU's and high-end overclocked socket 2011 stuff with the case filled with drives and fans and other bits. (Like mine.)

If I was in your situation I would go for a Corsair HX 750w unit, long 7 year warranty, good efficiency, good reliability, modular and it should out-live your PC so you can use it in the next one.

I've recently built my computer for playing GW2 and I'll just post some general resources I found out that may help you out (if you haven't bought the parts already).

When checking price parts, you have to check out this website: http://pcpartpicker.com/

It will compare prices on multiple stores and post deals for you.

Although some good advices have been posted on this thread, I would also post a build evaluation at this website: http://www.reddit.com/r/buildapc

Very helpful and knowledgeable people there. You can also find some links on the right part of the page with resources that helped me quite a lot on choosing my parts. EDIT: and on my build

If you're spending over $1000 U.S.D. then you really ought to have an SSD. In terms of overall performance it makes a huge difference and much more than say the difference between a low end quad core and a high end quad core for instance.

You know the 400R is a mid tower so it is smaller than the first case you chose? You should look up reviews of each part before you buy them. I spent a lot of time researching my case and GPU before I bought them.

Videos on youtube are good for getting a feel for the cases imo. http://www.youtube.com/watch?v=S-u7FdeLSMI

Graphics cards I would just look over reviews for all 660ti's if you are sticking with that. Personally I would jump up to a Gigabyte gtx670 since it is pretty much equal to a 680 and can be seriously overclocked. Especially if you plan to SLI it down the road. They beat a 690 without overclocking and can get up to 20k in 3d mark with an overclock. http://www.overclock.net/t/1253432/gigabyte-gtx-670-oc-version-hands-on/540#post_17182440

I'm a bit biased about the graphics card though since it's the one I went with. Getting almost 10k graphics score on 3d mark with no overclock.

And I wouldn't bother with an extreme6 and just get an extreme4. Only a few slight differences but it is only about $20 of a difference. Looking at the prices in the US is making me jealous.

Feels like I'm finally at that home stretch. Just waiting for the cash. 

Mobo

ASRock Z77 Extreme 4

Hard to find a reason NOT to go with this mother board. 

CPU

Intel Core i5-3570K 

For the past few days of comparing parts, prices and making decisions, I actually had an i7-3770k here. At the end, the budget I was looking at was a bit uncomfortable. Looking at some comparisons, I just decided that the performance increase wasn't worth an additional 100~120 over this.

RAM

Samsung 8GB (2 x 4GB) DDR3 1600

I actually had 2 orders of this for 16GB total. I think i'll be fine with one for a while. I see myself getting another in the future but for now, I doubt I'll need 16GB of ram. 

Video Card

GTX 670

Originally had a 660. With the budget increase, reading that most games are very gpu reliant, and knowing that I want to use 2 screen I said "fuck, let's move up 2 notches".

Hard Drive

Seagate 7200RPM SATA 6Gb/s 2TB HDD

For $90 and great reviews on Amazon and TigerDirect, it just seemed like a steal. 

Optical Drive

Samsung DVD Burner

Yes.

Case

NZXT Phantom 410 (Black)

Not a fan of the general look but I can get used to it. What I is like the position of the USB ports/buttons/etc. Don't think I'll ever need more than 3 5" drive bays. Has way more HDD bays than those 5" peripheral ones, and I see myself probably needing those in the future. Airflow plan seems good, had great reviews from both sites and costumers, and it's at a good price.  

Power Supply

Corsair Enthusiast 750W 80 PLUS Bronze Certified ATX12V

This really the only thing I'm not sure about. Seems look a good buy for the price.

OS

Windwos 7 (Home, 93$)

Haven't read much about window8. I have no problem getting used to something new like many people do. I just figured, win7 is a safe bet for a gaming rig.

I will be getting  USB Wireless Adapter, mouse and a Keyboard. Before these extras, I'm looking at ~1155 before tax and shipping (a lot of this will be shipping for free, it seems).

I've considered it. I do want one, but I won't go for it initially. Later in the year, I'll make some upgrades. That will be one of them.

I haven't tried the reddit idea yet but pcpartpicker was a very helpful site. Really cuts down the price checking. Thank you. I should note then when I'm looking at the cost of stuff or posting them here, I don't take into consideration the MIRs. Simply because they're not definite guarantees and I still need to pay the base price first and foremost. 

I completely agree with you on the motherboard and gpu choices. Also, I can't think of much reason not to go with the mid-tower case that I just switched to. 

http://www.youtube.com/watch?v=XTY4fD6cHss

Going by that video, at about 5:18 and 5:55, I shouldn't have any problem with huge graphics cards in the future. 

thanks for keeping this thread going. Def gives me ideas for the future.

Only disappointing is seeing how much cheaper some parts are in the USA compared to AUS lol.

Perhaps I should move lol.

That Ram is awesome. It's on a 30nm fabrication process, had a chance to play with a kit a few days ago and they overclocked to 2600mhz @ 1.65v with ease.
Heck I would use them in my current system if only the RAM had heatsinks that would match with my Case and Motherboard.

So don't change that. :P Would be a a fantastic kit of Ram overclocked if you are running an AMD APU based system that's for sure.

The PSU looks good too, but the Cosair HX 750w is not that much more expensive if the 7 year warranty, modular cables, higher power efficiency is worth it to you.

Just order from the US then? With the Aussie dollar so high even with shipping it's still good.
Just buy the big and bulky items from places like PC Case Gear or MSY. :)

Converesly, group buys can help lower those exhorbant shipping prices by splitting up the shipping costs between multiple people, did that for my current system and got each GPU for only $600 instead of the Aussie price of $750-800 when they were released.

Dgc, the 750W PSU you picked is $100 after rebate, non-modular. Right now Newegg has a sale on the 850W modular one for less:

CORSAIR Enthusiast Series TX850M = $115 - 15% off with coupon code EMCNJJJ29, ends January 16th - $15 rebate = $82.75
http://www.newegg.com/Product/Product.aspx?Item=N82E16817139029

If you don't care for the Assassin's Creed 3 / BL2 game bundle, you can get GTX670 for $300 US with free shipping after $40 rebate at NCIXus.com:

http://us.ncix.com/products/?sku=72414&manufacture=PNY%20Technologies%20Inc&promoid=1368

For CPU cooler (for overclocking), Thermalright TRUE Spirit 140 for $40 with free shipping is a beastly cooler.  You might want to measure the height from the mobo to the side panel of your case before ordering though.

http://www.nansgaminggear.net/ProductDetails.asp?ProductCode=TS-140

Performance vs. noise levels is nearly unbeatable among air or AIO water cooling kits for the price.

http://www.hardocp.com/article/2011/11/17/thermalright_true_spirit_cpu_air_cooler_review/4

I've got no problem with getting a bigger case so that cooler's size won't be a problem. I'm considering purchasing parts now just to take advantage of deals like the one on that PSU. Mmm... screw it. I'll order the PSU and that cooler now.