If you want to avoid long lines for museums in Italy, you can buy museum tickets in advance at http://www.florenceart.it/booking/. You just print your vouchers out on your own computer. We used this service the last time we went to Florence and were able to just walk right into the Uffizi without a wait. People without tickets waited for hours. We still needed to buy an excursion from Princess that provided the transportation from the port to Florence, but we'll never forget the opportunity to browse the Uffizi at leisure.
This is not something you would necessarily want to do for your first visit to Florence. After all, you want to see Michelangelo's David, but it's wonderful for a second or third visit.
I think there are other European cities where comparable services are available.
Hi Joe and Ivan
My partner and I were in Florence and Venice in 2002 and we bought a Venice Card. (www.venicecard.it) where you had unlimited vaporetto transportation, access to the Doge's palance and the Accademia museum. We didn't know about the tickets in advance for the Uffizi and waited to get in for hours! BLAH!