I will be in Amsterdam, France, and Venice in a few weeks. Do these countries use the same types of plugs or am I going to have to find separate ones?
Jamie, First, to clarify the terminology, it sounds like you're referring to Plug Adapters rather than Voltage Converters. What type of devices are you planning to charge? All of the countries you mentioned use the standard Euro Plug Adapters with two round pins for ungrounded appliances. If the appliances requires a ground connection, the Plug Adapters will be slightly different in each of the countries. You can have a look at the various types of Plug Adapters on the Magellans website. Happy travels!
If you are referring to adapters (which are the things that allow you to physically plug something into the wall), then yes. They are the same for all those countries for the ungrounded plugs. The Italian sockets have a different pin configuration for the grounded plugs, but any standard European adapter (like this: http://bit.ly/PKYtsv) will work just fine for your gadgets.
My experience with Italian electrical outlets is limited to a chalet I rented in the Alps, but this had a completely different configuration and required a specific adapter, which was easy to find at a local grocery store. I have heard that this arrangement is typical of older buildings in Italy, but not newer ones. As the others noted, the same adapter will work in the Netherlands and France.
My local Ace Hardware sells two kinds of "European" adapters, both with two round pins 19mm (~¾") apart. One is labeled No. Europe, and the pins are 3/16" in diameter. The other says So. Europe, and the pins are 5/32" in diameter. The southern one will work virtually everywhere in Europe; the pins on the northern one are too big for receptacles in southern Europe and will only work in northern countries that use the French or German version of the Schuko receptacle. I believe most adapters for continental Europe sold in travel stores are the southern type. The French style Schuko receptacle uses a grounding pin protruding from the base of the recess, but it is off-center far enough to clear the body of the plug adapter shown in Ken's post.