The Firenze Card costs €72 and is valid for 72 hours, offering priority access into 72 museums, churches, gardens and villas and special exhibitions (including the Uffizi) without the need to make reservations. The one exception is Brunelleschi's Dome at the Duomo di Santa Maria del Fiore, where ticket holders should book in person.
There's also a Firenze Card+ for an extra €5 that includes bus and tram travel (but not the Florence Airport shuttle bus) and Wifi in the city.
Children under 18 who are EU citizens get in for free with the card holder.
Whether or not it's a good deal greatly depends on what you want to see. Do check closing days as well so you don't miss out.
You can buy the ticket online and pick it up with a voucher at one of the sales points below , or just buy it there:
Uffizi (Porta 2, Piazzale degli Uffizi)
InfoPoint Turistico Stazione, Piazza Stazione 4
InfoPoint Turistico Cavour, Via Cavour 1r