Will you be building this PC? If not, I would stay away from big brand computers (e.g., HP, Compaq etc.)
If you want to get a good gaming PC and don't want to build it (though you should because it's cheaper and it's a learning experience), you can visit
http://www.ecollegepc.com/
It's a pretty good site in my opinion. You can choose a template from one of the computers they have and edit parts to your liking. Or, you can build one from scratch. Something that is beneficial is that when you're building your computer, the availability of parts change depending on what parts you choose. For example, if you choose a high-end graphics card, the PSU will change accordingly so that it has enough power to power the graphics card and your computer. That way you don't have to worry about having incompatible parts in your PC.