Phones with gigantic screens, such as the HTC Evo, have a tough time lasting a full day on one battery charge. This makes having a secondary charger almost essential if you're going to be out and about all day.
The Primo Cube is a little square charger that plugs directly into either a MicroUSB or MiniUSB jack on a phone, no cables required. It works with almost any smartphone other than the iPhone, which is stubbornly USBless. For only $40, something like this seems well worth it for owners of power-hungry phones. [PhoneSuit]