Everything in Europe (like most of the world) runs on 220-240 volts (as opposed to 120v in the USA).
Most electric shavers, notebook computer adapters, and battery chargers for cameras, iPods, etc. will be rated to handle 120 and 240. Read the fine print on the back of the adapter to doublecheck.
If your electric items are rated for up to 240v, then all you need is a plug adapter. You can get them at Radio Shack, any travel store, or at the airport. European plugs have 2 rounded prongs as opposed to the 2 flat ones in the States. Should only cost a couple of bucks.
In the rare case that you have an appliance of some sort that rates only 120v, then you'll need a small transformer. There are ones that are about 2x2x4 inches and usually automatically come with European prongs one one side (because why else would you need one!?) and an American-style plug on the other.