Whatever you do, no matter how funky it looks, don't buy a plastic case. They give poorer cooling, little EMR protection (both inside and out)and have a nasty tendency to fall to bits.
If you're building your own comp, it's worth shelling out for a really good case. It'll outlive the comp you put in it now, and it should do fine for your nest two mobos as well. Buy a tower; they tend to provide much better airflow and access to interior gubbinz, at relatively low cost to desktop real estate.
Heat retention is becoming a big problem with high end PC's, and for tgetting around this aluminium cases are the best, but they're not cheap...
This is one I'd like...... 5 5.25" bays, 5 3.5" bays... 3 case fans... c/w 300W PSU... front mounted USB ports...
But this one would be even better for a high end home workstation...
Did I ever tell you aluminium cases also happen to be well sexy?