Skech ArmBand for iPhone 5/5c/5s
It's nothing too fancy, but Skech's ArmBand for iPhone 5/5c/5s ($30) seems to be a fine enough option for strapping an iPhone to your arm. Available in black, with pink or grey accents, the soft material extends out into a band, that wraps back in and through a plastic clip, before using Velcro to attach to itself. The phone fits in a pocket with a clear plastic sheet over the front, and there's a headphone port cutout. There's also a slot for a key.