The Fever Labs LiPo shield, is designed to power your Arduino-type product without the need of being plugged in. The shield is stackable, and chargeable. It will provide a regulated 5V and 3.3v to power your devices.
A mini-usb connector allows you to charge from a USB port (while powering the connected devices). The typical Arduino footprint is supplied, and is stackable. This allows you to keep your valuable I/O ports open.
The LiPo shield is based heavily on the Sparkfun Power Cell.