Avvenimenti Florence (or Florence Events) is a great tool for finding out what is going on in and around Florence. They have everything on the site (exhibits, music, festivals, nightlife, etc.), dozens of listings daily, and you can search and sort things however you want. They also have simple lists like "Today" and "Weekend" for last minute planning. If you are a resident or tourist and want to know what's on in Florence, this is the place to start.