Whatever brand/style you choose -- and there must be hundreds of cases that will suit you -- I suggest you get a case large enough to accept an ATX-sized mobo, even if you end up getting a micro-ATX. That way, you have both of the most common sizes covered. After all, a good case can go on serving FOR YEARS and be re-used for MANY system upgrades down the road, so I'd get an ATX case for such flexibility.
A mid-tower ATX case will do (you don't need it TOO large) and an ATX case will hold at least 4-5 HDs (plus 3-4 DVD drives, and maybe a couple of 3.5" drives, too)...as you never know exactly what your future needs will be. Consequently, you should have a case that leaves SOME room for expansion, just in case.
Good luck...