Charging cables that are at your fingertips all the time just keep getting smaller and smaller. Back in March of this year, TUAW reviewed the ChargeCard, a USB to 30-pin Dock Connector charging cables the exact size of a credit card. Now there's the ChargeKey for iPhone 5 (US$25), an even smaller emergency charging cable that's the size of a house key.
Not surprisingly, both products are made by the same California company, Nomad. The design of the ChargeKey makes it a snap to attach to your keychain or to remove it for a quick charge. On one end is an open-faced USB connector, while a Lightning connector sits on the opposite end. If you're anywhere that there's an open USB port, you can plug in your iPhone (or iPad -- the ChargeKey is designed to withstand up to 3.1 A of current) to top it off.