The Friends of The Uffizi (or Amici Degli Uffizi in Italian) is a non-profit group founded in 1993 to support the museum after the terrorist bombing that damaged parts of the Gallery and some of its great artworks (details).
A lesser known fact is that by supporting the association, you can get free admission to a whole host of Florence's greatest museums, as well as not having to make reservations at the Uffizi or Accademia, or waiting in line.
The family membership is the best value - especially if you are spending several days in Florence and want to visit several museums.