[url]https://www.newegg.com/[/url]

Check out that website too, that is where I get all my computer hardware. Been using this site for the last 15 years, and can vouch for their service and products. 

[@Gareth]

And if you just wanna up your performance without building an entire computer, just get a graphics card (NVIDIA like those who posted above). And remember, if you up your graphics card, most of the time you need a bigger power supply as well. 

And then you can get those copper processor fans too. 

You can add little by little to your computer, and then transfer those parts over to a new case with a motherboard later, if you don't wanna drop $1,000 at once. That way you can increase your performance over time, eventually attaining a new badass dream-machine!