Well, it pretty much depends on what your budget is and what you intend to do with the computer.
My suggestion at current would be something along the lines of:
- Intel Core i5 or i7 processor, minimum 3GHz
- Atleast 8 GB of DDR3 memory, preferrably high-performance (XMS)
For the rest, well you've already stated what graphics card you intend to buy. And motherboard is basically just "a good board that supports your hardware". My recommendation of 8 GB minimum is to make things run smoother, and quicker load/unload of games/software. More memory = Less need to cache files on harddrive.