In addition to the costly wireless keypad, Sony is planning on introducing a new PS3 peripheral to market in December. The AC Adapter will be able to charge any two USB devices, from controllers to the Bluetooth headset to the wireless keypad. Heck, it can even charge the PSP-2000 and 3000. This will allow you to charge peripherals without having your PS3 turned on.
You can expect the peripheral on retail shelves in the second week of December for $25. However, remember -- you can save a bit of money by using your computer to charge your USB devices. You can plug a USB cable into your computer and charge a PS3 controller from there. Or, just remember to charge something while playing games on the PS3.