At last weeks Liberty Alliance Technology Expert Group F2F in Portland (which we hosted at Intel), I took a few of my fellow travelers over to the Intel store on campus so they could buy some Intel knick-knacks to bring home to the family. What we found there wasn't as geeky as some of my other gadgets, but very useful for international travellers...
An inexpensive (just $8.99), compact universal international plug adapter.
This one adapter works pretty much anywhere, and can be reconfigured like a transformer (the toy) to adapt to European and UK type plugs:
The sad part about this was that I was unable to find any marking/branding on the adapter to identify a source for it outside of the Intel Store (Sorry folks). I was able to find what looks like another plug designed the same way (can't say who copied who or even whether or not they are manufactured by the same, I'm sure Chinese, company). The closest one I have been able to find is an APC Universal Plug Adapter which you can buy for $15 to $30 at various places.
It's much better than the clunky adapters I've been using to date.
I should note that this is just an adapter. It is not a power transformer. You must have a power supply capable of handling 50-60 Hz and 110-240 Volts. Most portable electronics power supplies can do this nowadays, but you should check the power supply to make sure. There should be a label on the power supply or charger that looks like:
If you don't have such a range of inputs for your device, you will need a transformer (the power kind) in many/most foreign countries.