It seems like an easy question, and when posed as such those asking it clearly want make & model info so they can just add one to their wish list or pull the trigger and purchase it.  Purchasing a PC for almost any need should take a little more thought than that though, especially when it comes to multimedia processing needs.

Review Application Requirements

Understanding the hardware requirements for the software applications you intend to leverage is key.  Minimum specs, GPU & I/O driver support of course, and more should be taken into consideration.  This is also a great time to consider improvements throughout your multimedia workflows, looking for opportunities to save even more time with a new configuration (e.g. transcoding, data transfer, storage & backup efficiencies, etc.).