I think the iPhone 4 is way too sleek and sexy to hide inside a case. Now, maybe you can find a cool-looking case with some design that you like. But for my $$, I went with full-body Ghost Armor protection. Front, back, sides, top, bottom. You name it, it's protected (except camera lenses of course but even a case doesn't do that). $35 with installation at their kiosk at my local mall.
If you insist on a case, why not get one of those ones that has a built-in battery that doubles your iPhone's battery life? Form AND function.