I'd say get yourself the best motherboard you can afford (I like ASUS). Next, as much RAM as you can afford. Hook those up with at least an i5 CPU running at around 3GHz or better.
Hard drives are fairly cheap at the moment, get one with a SATA III interface for the best speeds. If you want to go nuts fast with boot up and general OS performance, get yourself a SATA III SSD with at least 256Gb on it and use this as your OS installation drive only.
Put all other software onto a traditional SATA III hard drive. Make sure your swap file is not on the SSD though.
Then get a graphics card which can play the games you want on at least the medium settings.
You should not have
to upgrade the graphics card for at least two or three years, unless something really radical happens!
FWIW here are my current PC specs;
- ASUS P9X79 Pro motherboard
- Intel i7-3820 CPU
- 32Gb (4x8GB) RAM with heatsinks
- 1Tb SATA III hard drive
- 256Gb SSD SATA III hard drive
- Corsair Hydro H60 liquid CPU cooler
- AMD HD7970 Sapphire Vapor-X 6Gb graphics card
- Antech case
- Gold certified 850W PSU
- 3 x Packard Bell viseo 230ws on tri-monitor stand