Viv,
I have a few suggestions to add.
First, it would be a good idea to clarify the terminology. In order to connect North American appliances to outlets in Europe, you'll need a Plug Adapter which will differ depending on which part of Europe you're in. The typical Euro style uses two round pins while the U.K. model has two or three large rectangular pins. It's a good idea to pack at least two Plug Adapters in case one is "misplaced" or whatever.
If the electronic device is NOT designed to operate from 220 VAC electrical systems, then you'll also need a Voltage Converter. These are often supplied with an attached Euro Plug Adapter.
You should check the specifications on EACH DEVICE that you'll be travelling with, and note the Input Voltage ratings. If these state "100-240 VAC, 50/60 Hz", these will work fine in Europe with just a Plug Adapter. If these state "115 VAC, 60 Hz" then you will also need a Voltage Converter.
If you need a Voltage Converter, it's important to choose the correct method of conversion. As the others have mentioned, electronic products such as Nintendo Chargers, etc. require a Transformer converter. While these are available in various sizes, Transformers are inherently heavy so a 50-watt model is about right for travel. These DON'T have the capacity to power hair dryers or other high-wattage appliances.
For high wattage devices, a solid-state Converter is appropriate. These don't produce a "clean" sine wave but for simple heating elements or whatever, they're usually adequate.
One important thing to note is that most travel Voltage Converters are not designed for continuous duty operation. It's a good idea to unplug them when charging is completed.
You might want to check www.magellans.com as they have a good selection of Plug Adapters and also an auto-switching Combination Voltage Converter.
Happy travels!