I have decided to build a new rig  , here's  what i 'm thinking of so far.

MOBO - Gigabyte G1 Sniper3

GRAPHICS CARD -  ASUS GTX 680 Direct CU II TOP

MEMORY -  8GB G.Skill Trident X PC3-22400

HARD DRIVE - OCZ Vertex 3  240GB

PSU TX850 V2 850W

CPU - Core i5 - 3570K with a Corsair H100 WK set

 what do you think ?

looks good, though I don't know if that motherboard is compatible with the processor. Don't know much about intel

Thats because they aren't. The processor is socket 1155, the motherboard is socket 2011.

To the Op... If you want to go socket 2011 then get the Core i7 3820 if you don't intend to overclock, Or the Core i7 3930K if you do intend to overclock.

Or converesely, get another motherboard, but with that said, Ivy Bridge overclocks worse than Sandy Bridge, so you could pick up a Core i5 2500k or the Core i7 2600K.

Also, what resolution are you gaming at? If it's only 1920x1080 resolution, then a Geforce GTX 680 is a waste and complete overkill, if you are gaming at 2560x1440 or 5760x1080... Then you may want two of the Geforce 680's or 670's.

As for drives... I find having a smaller and cheaper SSD is the way to go, something like a 64gb - 120gb for the Operating System and applications.
Then get a fast 1tb or 2tb drive for games and an External USB 3.0 drive for storage, you will notice bugger all in everyday usage between different speed SSD's, the MAIN benefit is the access times.
And loading most games is sequential reads anyway so the benefit is minimal for games.

And lastly... If you are only running single GPU, no need for a 850w PSU, you could get away with a 650w or 750w PSU easily enough, heck I used to run 2x Radeon 6950 2gb cards unlocked into 6970's off a single Corsair HX 750w just fine, but if you can cut down on the PSU wattage and get a higher quality HX or AX model, that would be better. You save money on the power bill too! (Not to mention modular, longer warranty...)

Sweet jesus, the only thing I'd change is the CPU to an i7. And I guess what these guys are saying with the motherboard.

so  i7 3930K for that Mobo or how about a gigabyte GA -277X -UD3H -WB Wi-Fi  for that CPU, as to the PSU I was looking more to the future  and adding another gpu down the track  and  have a 1TB drive  on my old  PC   , thanks for the advice.

From what I have read, there is no need for an i7 for gaming performance. Beyond an i5, there is very little gain, and the graphics card become the deciding factor, so I actually think that is the right CPU to choose

I am building one myself, but haven't fully decided on the build

Motherboard - a z77 one
CPU - i5-3570k
GPU - 670
RAM - 8 GB (Corsair maybe?)
Storage - HDD + SSD combo
PSU - about 650W, but enough headroom for a 2nd card
Case - Sharkoon Tauron

Any advice would be welcome

You can find a GTX 680 that's in stock? Please link.

Either would do fine.
The 3930K is a beast though, should last you many years being a 6-core processor, some games also *do* benefit from the 2 extra cores, Civilisation and Battlefield come to mind.
I personally wouldn't listen to anyone who says that a 6 core processor is a waste, people said the same thing about Quad-Cores when the Q6600 was launched over 5 years ago, the Q6600's clocked to 3.6ghz are still running games like Battlefield 3, where-as the Dual-Cores pretty much went in the bin, the Q6600 turned out to be an excellent long-lifed chip.
Also what kind of monitor set-up are you using?

I found it through a search on static ice

If you can afford it then it's good but in terms of "bang for your buck" it's a case of diminishing returns, especially if you get a quad core chip with hyper-threading.