I use this:

Kensington 33362 Ultra Portable Power Inverter 150.
http://www.amazon.com/Kensington-333...0379769&sr=1-2

The advantage of this is you can plug anything into it: it has a normal 3 prong (us) plug. I use it to charge my phone, headset, MP3 player as well as my laptop on the plane.

Disadvantage: you still have to carry your computer power adapter as well.