I reported earlier how I no longer take battery chargers and voltage adapters with me on trips. That's because most devices now can be charged through their USB cable: I connect my MP3 player, Palm T|X, etc to my notebook computer's USB ports for overnight charging. (Just my camera doesn't recharge that way.) The notebook computer's power supply handles all the voltages and cycles (Hz) of the world.
Now USB charging has come mainstream. Engaget reported on a power plug that has two USB ports. You plug it into the wall outlet, and then plug your USB devices into it; that would be handy when you don't take along a notebook computer.
Imaging Resource today reports on a battery charger that's similar in concept: Duracell's Power Gauge Charger features LED indicators that display the charge status for each battery, so that you know when each charge will be done. It also has a USB port (just one?) for charging USB devices.