Desktop that won't lag on Minecraft?

Building your own is the best way to do this without getting too expensive. For no lag on MC, I would recommend an AMD FX 4300 (or better) or a core i5 2nd gen or better for the CPU. You'll also need at least 6GB of RAM for absolutely no lag. For the GPU (this part is huge that a lot of people tend to neglect for some reason), you'll need a NVIDIA 550 or better or a Radeon HD 6000 series or better. The HDD can be just about anything for MC, but I would recommend a WD Black of your desired size.

With Epic Computer Nerd Skills.

Just buy an alienware and show it off at how much wealth you have.