My roommate has owned both the 320 and the 603 cases. These are some of the nicest cases I've ever seen. The 320 is great because it's small enough to fit in most desks and has nice insulation to absorb some of the heat from your cpu built into the case. Also it's toolless so you can take it apart without tools.
The 320 is my favorite though. The black one is incredibly stylish and talk about heavy, this thing weighs about 30 lbs empty! It's just an awesome case and it's HUGE. If you want a nice open case with tons of room to work inside of it, this is the one for you. Comes standard with 300w athlon power supply and will cost you about $98.
divinemartyr