What do you consider to be "must have" technology while traveling in Europe?

I prefer an iPhone over an iPad for its compact nature, email, Internet, mapping, photographic capabilities. Small hi res pocket fitting camera, several long lasting double A batteries and a euro USB wall adapter. Plus a external battery charger. This is all I ever bring and it meets my needs to keep up on my professional life and touristic endeavors.

I'd say a camera--a pocket point and shoot or maybe even a Flip-style video camera. The Flip is handy because it runs on AAs, so there's no need to recharge... My idea of traveling light is one carry-on size bag and staying in hostels. If that is similar to yours, I'd leave the rest of my electronics at home.

I always have my phone and my tablet with me. My tablet is connected to the internet non'stop. I use http://goo.gl/u4hFMz It provides very cheap web access across the world, but in Europe it's even cheaper. Having internet while travelling is priceless - you can check everything from travel route to tickets, from opening hours of museums to good restaurants in the area. And since you have these two gadgets with you you also have your music and a camera.

We went to Europe for two weeks last fall and these are the bits of technology I found valuable. - iPhone - for checking news and email on the hotel's wireless network at night.  For sending text messages back home (AT&T offers a reasonable text messaging package for about $50.) For checking subway station maps. For locating on a map where we were and where we were headed. (See below) - Mtrip Travel Guide app - the apps ran on my iPhone and they have them for most major cities around the world.  They tell you about restaurants, hotels, and attractions but they also plot where you are on an off-line map which was invaluable.  The normal "Maps" app on an iPhone requires new maps to be downloaded to your phone as you change locations.  The "data" for the on-line maps is supplied by a European cell phone company, plus a roaming fee, and the charges can quickly run into the hundreds of dollars.  The off-line maps within Mtrip are downloaded to your phone when you buy and install the app so you incur no data charges when you're using the app in Europe.  Really valuable app. - Travel Zoom point and shoot camera - most point and shoot cameras have a realitively small zoom lens (3x to 5x.)  These newer "travel zooms" have much more magnification (15x to 18x.)  When you see the Eiffel tower off in the distance, you can fill the frame with it with a travel zoom.  If you see some cool detail high up on Notre Dame, you can get it with a travel zoom.  These cameras are comprable to a 28mm to 400mm lens in the 35 mm world but you can still fit them in your front pocket. They also shoot HD video so you don't have to take a seperate video camera.  They are the best of both worlds, in more ways than one.  I bought a Canon SX230 before I left and loved it. - All-in-one plug adapter - I bought one that could convert to any outlet and it worked well.  I think I bought it through TravelSmith. - European power strip - because many hotels in Europe have only a couple of outlets in a room, not enough to recharge iPhone, camera, and run wife's blow dryer, curling iron, etc. - I took an iPad as well just to be able to look at internet more easily but probably could have gotten by with just an iPhone.

A usb pen for internet and to save files. An extra SMD card for your digital camera. Definitely a plug adaptor like previously stated.