Most things these days are supplied with power supplies and chargers that can cope with supply voltages of 100 - 240 V. That will cover most of the world! If you buy anything, check the input voltage marked on it. Don't forget plug-top power supplies and chargers will be useless even if they are multi-voltage as they will be USA plugs.

The main issue therefore is display standards - so anything that is designed to be displayed on a TV - DVDs, console games, will not be 100% compatible with European equipment. lots of European TVs will display the American TV standard, and DVD players can be modified to play American discs, but unless you know for certain your kit can cope with non-European discs it's not worth the risk.

Ceri's comment about laptop keyboard layout is a very good point, it would be very different.

I'm intrigued myself about Nintendo DS compatibility, I may research that some more!