For a good basic system, get a motherboard with socket 1156 or 1366 (1366 is better for future updates), Intel's i7 -processor, ATI's HD5850 or HD5870, around 4GB of DDR3 RAM and ~700W power supply. (plus all the normal stuff) That should be more than good enough for current and future games. Although, depending on your budget, you may need to tweak the setup.
Also, order the components in parts and then build them together yourself or at some local computer store. Most PC's out on stores have low-end graphics cards and HUGE processors which only don't make the PC cost enormous amounts, also causes a huge bottleneck for the system and it therefore runs at slower speeds than normal, with proper components.