I always suggest this site for those who are new to the PC scene. http://www.hardware-revolution.com/computer-systems/gaming-pc/
Reasons for it:
Offers the best bang for your buck and where to get it
Fits pretty much any budget
Forums are very helpful with nice, friendly people who welcome any and all
only thing about this company i hate is their customer service. the computer is awesome! but i had to send it back twice to get things repaired that were faulty. once on arrival, and once after they "fixed" what was wrong. now that im passed that stage they have good builds. Even if you dont want to buy from here you can read the forums they have. A LOT of helpful people that are willing to look at builds and give you better advice on where to get parts.
If you have some computer knowledge and dont mind trying to piece together parts, http://www.newegg.com/ has always had the most quality parts for as cheap as you can get them.