Well, I ended up getting the aluminum case from e13ctron. I really wanted a bumper-style case, but something a bit more solid than the Apple one. They have a ton of colors, and offer the cases in matte, brushed, or chrome finishes. I went with plain brushed aluminum (I think it has some sort of clear finish on it, but it looks like bare metal) because I felt that it most closely matched the design aesthetic of the naked phone, which I rather like.
The case itself is very well-made, with precise machining and no rough edges. It adds about the minimum amount of bulk possible, but still provides a bit of a lip on the front and back, so that you can set (or drop) it on a flat surface without making contact with the glass. Inside the case, the phone does not actually touch the metal frame. instead, there are two plastic rails that run all the way around the case, top and bottom, cradling the phone. It’s a really nice design. Buttons are recessed just enough to keep them from getting pressed accidentally in your pocket, but not so much that they are hard to press. We’ll see how much I like it after using it for a while, but initial impressions are very good.
It does add some weight to the phone. Not a lot, but a little bit more than a plastic case would have. Not really a big deal for me–the iPhone 4 is pretty hefty, anyway. Pics:
With e13ctron case