You'll want to look at Bitfenix cases, and perhaps certain Corsair cases. They're the only ones I know of that pull off an elegant and simple look, without stacking on a bunch of mesh and ruffles as Coolermaster or Raidmax cases (for example) tend to.
Try looking at the Merc Alpha or the Bitfenix Shinobi/Shinobi XL.
Some Antec cases are also quite nice and clean looking, without sacrificing function.