Crank Brothers B17 Multi-Tool
The Crank Brothers Multi 17 multi tool is a fantastic gadget that will get you out of any bike (and possibly non-bike) related scrape when you're on the move. It's durable and reliable and contains a brilliant range of wrenches and other tools. The integral chain tool is great - with a deep and secure single plate, a textured surface for grip and a compact body which acts as an effective handle.
The Multi 17 has a great overall design, with curved edges and a rubber band to stop it rattling around in your saddlebag.