From: Ontario, Canada
Here are some tips, but beware I am NO computer expert, have built about 7 here in my house and I do it as a hobby with no formal computer tech training or courses whatsoever.
Buy the biggest Hard Drive you can afford, you can NEVER have too much hard drive space. But from experience I since my last build have purchase a 120 SDD Hard Drive for the operating system and main software programs only and have 3 1TB extra Hard Drives where I store all my videos, games and music, pictures etc.....If the computer ever crashes I never loose any of my stuff as they are on other HDs. The only one is the "C" drive which can easily be reloaded. Now I said SDD as you will notice a significance increase in speed on loading or booting up plus accessing any of your games that only require a little of the C drive even though they are installed on other drives. You can partition one HD and operate that way. Just so much simpler to have all your own stuff on other drives for security purposes of not loosing anything.
Never install less than 8 MB of Ram if you are installing Win7 Pro 64bit, I always have 16 on my gaming computer and it may not be necessary but RAM is cheap now, so go for it.
I strongly suggest you get a Blu-Ray player/Burner as Blu-Ray will be the only thing in the next couple of years as DVDs will slowly be going the way of the Beta Players. You can still use it for DVDs either loading games, watching videos and burning DVDs but at least you will already have the Blu-Ray drive to watch Blu-Ray films (unless you already own a Blu-Ray player or PS3). Trust me you will be ahead of the game by far. Of course with the proper software (I use Nero 12 Platinum) you can also burn Blu-Ray discks.
The Intel 1-5 Quad is more than sufficient for gaming plus it is reliable and is proven to work well.
Motherboards: you can save $ on a sound card if you get a Motherboard that already has a sound card and the optical cable plug in. Now for most non-music experts it works just as fine for everyday use than adding an extra sound-card. Again all depends how serious you are about sound quality. I and many of my friends see no minuses using the one with the motherboard but make sure it has optical sound plus to plug into your speaker system.
Cases: they vary in price and quality but I suggest you do NOT purchase anything with water coolant as they are very complicated to repair and maintain and I can only fathom what would happen if it burst inside the case. Just look for a Case that has a minimum of 3 fan systems in 3 different locations in the case. Make sure if it a quieter model case as some can be very loud when the fan are spinning.
Power Supply: I do not recommend anything below 650 watts. This will enable you to run anything plus have tons of power to run any other hardware you may decide to add at a latter date.
Video Card: this is where some people go cheap and I keep reminded my friends that the best investment you can do to your gaming computer is go as high as you can afford. I stick to NVidea cards all the time as I had bad experiences with ATI but that is a personal choice. I recommend that GTX 560ti and above. They are significantly cheaper now then they were when I purchased mine. Best video card I have ever used fro gaming. You do not even need to sli 2 cards. It was at one time better but not anymore. One powerful card is sufficient now and is still way powerful for everyday gaming and beyond.
I am hesitant to recommend specific brands as I am in Canada and not sure where you are so prices may vary greatly. I do remind you that I built my own computers and my families solely as a hobby and from the expertise of friends and my online gaming companions, so not a computer techie here, just having some fun building them. Remember if you spend 5 to 8 hours a day on your computer and enjoy it like hell, spending a little more than you budgeted is not a bad thing considering you may use it more than your expensive car...............
Lastly: the only thing I do not personally do myself is install the Chip into the Motherboard, I always get the shop where I purchase all the hardware to do that for me for like $20.00 as using the thermal glue with the chip is a little scary for me plus I do not damage the "heart" of the computer. The rest of putting it all together I do on my own and it takes less time than loading all the Operating System, updating, virus checker, Drivers etc....
Hope I was able to help you out a bit and good luck, nothing more satisfying than booting it up for the first time!!!
It is much harder to think about doing something than actually doing it!