We were in Florence last August and we really enjoyed these two restaurants.
The first one (a small, local place) we visited several mornings for coffee/cappuccino and croissant for €5-7. The other menu items look great as well!
Budellino Winebar & Caffe
We enjoyed lunch and dinner at this restaurant and it was recommended to us by several RS posters.
Just be sure to make reservations!
La Bruchetta