Most places you visit were not built for USB devices. You’ll see standard power outlets everywhere, but only recently have USB outlets started being built into homes. Phones and tablets usually come with an AC adapter, but they are small and easy to lose. Android Area has a couple of good deals on USB charging hubs that won’t require an AC adapter.
The Aduro Surge Protector easily plugs into a standard wall power outlet. It gives you 6 standard outlets and 2 USB outlets. This is a nice way to bring your old power outlets up-to-date. You can simply plug in your phone without the need of an AC adapter, plus power a bunch of other devices. It’s available for $19.
The Dyconn 5-port USB charger also plugs into a standard wall power outlet. It looks more like a standard USB hub with a long cable and a box containing the USB outlets. You can charge up to 5 devices at once. This is a great accessory to have for travel, especially hotels that are typically low on outlets. It’s available for $21.