Florence museums

You will save yourself a lot of time if you buy these in advance - they are probably the two most popular sites in Florence. Don't take a chance you might spend half your day in line, especially if you're only there for 2 days -- book ahead.

Seconding Chiara's advice, Genie; I'd buy your tickets ASAP so you have the greatest selection of remaining time slots to choose from and can skip potentially long ticket lines when you arrive (you will have to pass through routine security checks). If you don't have the official ticketing website, here it is:

http://www.b-ticket.com/b-ticket/uffizi/default_eng.aspx