There are two camps of iPhone users: Those that use a case, and those that don't. I'm squarely in the former after my share of iPhones over the years. In fact, I always use a case with my iPhone because it's a miracle of miniaturized technology sandwiched between two pieces of glass.
I've been testing the Seismik case ($35) from Lunatik — the same folks that pioneered the iPod nano watchband — for a few weeks, and I'm impressed with the level of protection that it offers. Seismik utilizes the same patent-pending Impact Truss system found in the company's Taktik cases, providing serious drop protection for your iPhone.
The unique air cells around the perimeter of the case absorb impact and direct it away from the iPhone. I've dropped my iPhone 5 a couple of times while using the Seismik case, and it suffered no trauma. In fact, it actually bounced after landing on the corner of the case after a short drop.
The open cell design of the Seismik case reminds me of non-pneumatic tires (NPT) like those developed by Polaris for all-terrain vehicles (see this YouTube video), and it works in much the same way. In addition to the cushioning air holes, Seismik also features a semi-transparent hard shell back panel and openings for the camera, flash, speakers, and buttons. The volume buttons are a little harder to press with the case on, but I chalk that up to a trade-off for the additional protection.
Seismik attaches with a simple snap-on design and adds only a minimal amount of heft to the iPhone 5. As with all impact cases, Seismik adds to the footprint of the iPhone, resulting in some compromise. Mine, for example, won't fit in the Elevation Lab dock that I have on my nightstand, but that's a price that I'm willing to pay for the additional protection. Although its width is increased, Seismik doesn't add much thickness to the iPhone 5, allowing it to preserve most of its pocketability.