I recently built a gaming pc from parts, as my laptop was struggling to run the latest games even on very low settings. I did some googling and came to the obvious conclusion that building a desktop for gaming is way cheaper than trying to buy a new laptop, and the desktop gets way better performance. In fact, this makes it so that I can stretch my laptop for a few more years, as it's only used for web programming at the moment (and it's plenty fast due to its SSD).
At the end of this article I'll be listing all the parts I used for my build.
Before Building a PC
You will need to take a few precautions. I recommend using an anti-static wrist-strap. They are about $5 and save you from frying your much more expensive components due to static electricity. Wear it like a watch and clamp it to an unpainted metal part of your computer case. I used the Belkin Anti-Static Wrist Band for my PC build.
Get some diagnostic software. I recommend the Ultimate Boot CD. This will come in handy if you have problems getting your system to boot or problems with it crashing. It has diagnostic tools for CPU, memory, hard drive, etc... I used it when troubleshooting my build and I found that it was just a bad memory stick causing all my issues.
Plan your build
Next you'll want to spec out exactly what parts you'll be using and ensure they are all compatible with each other. A good site for finding parts and getting the best price is PCPartPicker. If you need help deciding on a PC build that fits your budget, head on over to BuildAPC. I had them recommend me a gaming PC build for my budget. They can also help you with advice on how to actually put the parts together.
Actually Building a PC
I recommend that you build the PC with a TDD mentality. Put in only the parts necessary to get it to POST successfully. From then on, I would add individual components and test them with your UltimateBootCD. Only after all the hardware passes tests should you install an operating system and drivers.
I am recommending this approach after having done it the wrong way myself. I put everything in and the operating system before doing any testing, and I was having random crashes going on. It took hours of troubleshooting: read more about troubleshooting my build.
What Parts Did I Use?
So far I've only used it for running the UltimateBootCD.
I like this keyboard because it lights up: red, blue, or purple.
I bought this ram after I had to return some G Skill ram that was bad.
The important part here is that it's the 2500k edition, which will allow overclocking if you're into that.
Be sure your power supply has enough watts for your pc build (and supports crossfire or SLI for your graphics card).
This graphics card was said to be unlockable to a 6970, but my particular card was not. However, it's still a very powerful card.
This motherboard has some overclocking options built in.
This case has great cooling, and is relatively quiet in my opinion. If you need quieter, I would replace the hard drive fan with a quieter one. It's the loudest fan on this thing.
With hard drive prices the way they are now I wanted to save some money and 500GB is plenty of space for game files. Some people recommend a SSD for gaming boxes, and while the performance will certainly be better, I haven't noticed load times being much longer with this disk. It's fast enough.
Parts I Had Already
Though I already had this monitor at the time, as I use it for work, I'm listing it here because I highly recommend it. The picture is great, it's height-adjustable, rotatable, and can be mounted on a wall or monitor arm. If the new price is too much for you, you can always find a refurbished one for about $300. Most importantly the resolution is 1920x1200 not 1920x1080 like most monitors these days.
This is the best left handed gaming mouse I have found on the market today. It also has drivers for both Windows and OS X. The only annoying thing about it is that the manufacturer switched the left and right click. So out of the box left-click and right-click are switched. Luckily this can be adjusted with the drivers. There are surprisingly few options for left-handed gamers, and the symmetrical mice don't do it for me.
All said and done this build cost me $922.79. It runs current games on Ultra High settings, and has some room for overclocking or adding a second video card. It is also said to support Ivy Bridge CPUs (when they come out).
Interestingly, building this way allows me to buy a cheaper laptop next time I replace it (I don't have to care about the graphics card in my laptop). So overall it'll work out cheaper, and I end up with a much better gaming experience.