PC Gamer magazine still keeps an updated low, mid, and high end build list on their forums
right here.
Whenever I build or upgrade a PC I start with one of their lists and modify it as I see fit (NVidia GPUs as opposed to the Radeons they usually use). All of it is linked to
pcpartpicker.com so no matter what you'll get the best deal. They also have guides and a very helpful tech savvy community that will help you with just about anything.
Hope that helps!
Edit: Fixed links