Scoobes did a pretty good choice of bits.

About future proofing your machine, Intel's Ivy Bridge (out in 2012) will work on socket 1155 (Intel 2500K) so you could upgrade if necessary and your boards get a new BIOS (so get a mid-to-high end motherboard, not a cheap one).

About RAM, 8GB kits are cheap enough to go for it and later on you can get another 8GB for a total of 16GB.

Some of the software you will use might use CUDA, so the logical option would be to get an Nvidia card. No future proofing here, in 6 months there will be better ones.

To choose the power supply you can use a calculator like this one: http://www.coolermaster.outervision.com/advance.jsp

One more thing, if you are going to work with images, don't use a monitor with a TN panel! Colors are not as accurate as they should. IPS panels are quite cheap nowadays and aren't that bad at gaming. Check http://www.tftcentral.co.uk/reviews.htm or http://www.flatpanelshd.com/reviews.php

You left off the most important piece of information, budget

List the total budget and then prioritize your list of hardware aspects in relation to which functions you'll be using most as a system.

ie. You encode video or audio regularly = prioritize CPU and memory, both RAM and HDD storage. For dedicated encoding systems/workstations, it's not unreasonable to spend half the budget on CPU alone.
VS
You mostly game but still claim to be using your gaming system for "productivity" = prioritize your gaming VGA card(s). For extreme gaming systems, it's not unreasonable to spend half the budget on the VGA card set up alone.

Either of the quick examples would be made better with the addition of a SSD boot/application drive, as would most systems used for anything but mostly web browsing and e-mail. For OS and apps, I'd recommend 120GB minimum. Again, it all boils down to budget and prioritization. You have over $1000 for a 500GB SSD? Go for it.

CPU wise, the i7 2600k is the best bang for buck amateur/hobbyist workstation CPU with the i7 2500k being the best performance gaming CPU on a bang for buck basis. The extra $100 in a gaming rig would be naturally better spent on more GPU power.

The Extreme CPUs and Xeon CPUs yield diminishing returns relative to the added cost. Not an issue for those with deep pockets, professionals, companies or art schools, but if you're not a working professional, it's hard to justify paying $1000 and more for a CPU that will be replaced in 2-3 years.

Liquid coolers aren't much more expensive than the largest/most efficient air coolers if you're looking at enclosed coolers that aren't custom built (your $200+ cooling solutions). The main advantage is that the cooling element is not cluttering the inside of the CPU case, which can cause build issues when assembling systems (most giant air coolers are engineered well enough to avoid these, barring RAM sticks with oversized cooling fins).

RAM is so cheap currently that even a moderate budget system can swing 16GB (currently well under $100) for dual channel MoBos. For the triple channel MoBos, 12 -24GB. It goes without saying that unless you're working with extremely large files and/or running multiple production apps simultaneously, you don't "need" 16-24GB of RAM other than to say you have 16-24GB of RAM.

It's tough to give you a convenient list of everything to buy since it sounds like you're building a complete system to include all components outside of the CPU case starting with nothing. Either way, your #1 criteria should have been budget, assuming you're not charging this on an open corporate credit card account and/or are not independently wealthy.

i have enough like $3000-4000

the fact that i didn't mention it is because in india almost all things cost 1.5-2times

also because all the things like CPU and GPU have verious different price categories like Xeon,Core i7 extreme,Core i7.thats why i asked which will be enough for me or is there need of more

what do  dual and tripple channel ram motherboards mean?

the same for pci-e slots,what do channels mean

and speed mean liek 16x or 8x?

my budget is plenty around $3000-4000

but i am not looking to brag or just build a giant system and also not going for a alrite for now system and then outdated fast or apps don't run.

keep in mind,i am form india where these things cost more

It's best to work through these things step by step, first decide what kind of CPU/GPU you want/need then build the rest of the system around that

snakenobi said:

In simple words, it's the nº of channels the CPU use to "talk" with your RAM. More channels = better speeds but also more latency. More: wikipedia

Most CPUs use dual channel, the "old" Intel's i7 (the likes of 920/930, 950 etc.) use triple channel while the new i7 (3930K) go with quad channel. When buying the RAM the difference is that dual channel kits comes in packs of 2 modules, triple channel comes in packs of 3 and quads in packs of 4.

The combo CPU-chipset (like those of X79, Z68, P67, 990FX, etc) talk to the devices that you install in the motherboard via a series of lanes. This number of lanes are finite (X79 gives you 40 PCIe 2.0 lanes while the 990FX has 42) and are spreaded into the different PCI slots that comes with your mobo. Simply put, the more the better. But be careful with the names, a PCIe 2.0 is different from a PCIe. To learn more: wikipedia

This multiplier tells you the number of lanes the PCIe uses (16x = 16 lanes, 4x = 4 lanes). Every motherboard has at least 1 PCIe 2.0 x16, and this is where the graphics card goes. If you go with SLI/Xfire you must look at the other PCIe slots. When using 2 Gfx cards some boards will split those 16 lanes into the 2 cards (8 for each one). The difference in performance is usually negligible. See more examples here: http://www.hardocp.com/article/2010/08/23/gtx_480_sli_pcie_bandwidth_perf_x16x16_vs_x8x8/

I hope it helps.

Don't fuss over the differences between dual and triple channel memory. It's tied to the CPU/socket you end up buying.

The original Nehalem i7 CPUs used 1366 socket mobos that utilized triple channel memory which meant buying RAM modules in sets of 3 to utilize that function and the incremental increase in memory speed.

Dual channel memory is used in the current 1155 socket based Sandy Bridge CPUs like the 2600k and 2500k, meaning you buy RAM modules in pairs. 

The difference is for all intents and purposes negligible for all but the most memory intensive functions. 

LGA 2011 socket CPUs (Sandy Bridge E) is the replacement for LGA 1366 and uses quad memory channels (buy RAM sticks in sets of 4).

The PCIe channel speeds are again dependent upon the CPU/socket you buy. More memory lanes (16x VS 8x) simply means less shared memory bandwidth. You can have more PCI cards installed with fewer restrictions on shared data pipelines. For most users, it's really not a huge issue unless they are running multiple VGA cards in SLI/Xfire mode along with any other PCIe cards they may have installed. 

How much you spend on a system is more or less dependent upon how long you intend for it to last or more importantly, stay current if you want/need a top of the line set up. So unless you have a consistent regular budget for updates, blowing everything on the best, most current components today might not be so great in three or so years when you find yourself needing/wanting upgrades because your $4000 system is now being matched/outperformed by a $2000 one. 

Total budget should factor in for all the other components outside of the CPU case like displays, good keyboard/mouse, sound system (for entertainment systems), and of course your software licenses for any professional apps you're planning on buying, assuming you're not planning on spending everything on hardware and then just pirating all software. If you're a student, those licenses are a fraction of the cost, which doesn't seem to stop students from pirating software anyway, but the whole issue of software licences/costs still needs to be thrown out there when talking budget, assuming one doesn't have a separate budget for that as well. 

But the legit concern about buying components that will be outdated in 2-3 years should be dissuaded by saying that even 3 years later, LGA 1366 based systems are more than just capable (just not cutting edge); there's just no point in building one today if starting from a blank slate since there are better options available.

If one was just spending $4000 US on components purchased in the US at US prices on the CPU only (meaning just the computer case with all installed components), you'd be building something more like the following Falcon Northwest Mach V system listed below. 

http://reviews.cnet.com/desktops/falcon-northwest-mach-v/4505-3118_7-35061104.html

Read the review to give you an idea of what is current cutting edge as well as measured value of buying/building such a set up. 

Seeing as how you're buying parts in India, it goes without saying that your mileage per $ will vary greatly. 

i7 2600k/2700k is all and more than most of the population needs for a gaming/productivity system. For gaming, the i5 2500k performs about the same for $100 less. Unless you're building a server, which you aren't, you can skip the Xeons. 

If you want the most current and are willing to spend more on the CPU/motherboard, the i7 3930k was recently released as a part of the new line of CPUs using the new socket LGA 2011. It's a $600 CPU with limited (but excellent) motherboard choices that currently don't dip below $300 at the bottom end and are closer to $500 at the top.

http://www.amazon.com/dp/B00603QXPM/ref=asc_df_B00603QXPM1837559?smid=ATVPDKIKX0DER&tag=hyprod-20&linkCode=asn&creative=395093&creativeASIN=B00603QXPM

how long will 6 cores processors suit as intel takes new processors every year and they could give 6 cores next year for normal processors such as i7 and i5 other than extreme processors which will go higher

also i7 3930k in india costs $1200

i might still go for it though there should be value and are current applications even using that much,if not then it will support me for alot of years so i might buy it