What characterizes these early works of Renaissance sculpture is a new naturalness and humanity to the figures represented - for we're almost always talking about standing male figures. Donatello introduces a naturalistic standing pose in which the weight is on one foot and the hip juts out (called contrapposto), and his faces have personalized features and apparent mental depth. Compare this to works by his contemporaries, which tend to be rather decorative and plastic.

Other brilliant works of sculpture from the first decades of the Quattrocento can be found in the Museo dell'Opera del Duomo (temporarily partially closed for restoration), since the Operai, the people in charge of the Cathedral works, were the major patron of sculpture in the city for many centuries. Thus you can see the late Medieval reliefs made for the Belltower, as well as later works by Donatello here - like a striking carved wooden figure of Mary Magdalene that Donatello made for the Baptistery.

Another obvious location of sculpture in Florence is the Bargello, the national sculpture museum. Donatello has a whole room named after him - and some pieces made for Orsanmichele ended up here too - but you'll also find originals of some works that were displayed in Piazza della Signoria. There are also later Renaissance sculptures, like Michelangelo's drunken Bacchus and Verocchio's David.

Sculptures in the Loggia dei Lanzi, Piazza Signoria

Finally, Piazza della Signoria and the Loggia dei Lanzi are an open air sculpture museum. The Loggia contains Roman as well as Renaissance pieces (see this article for a description of each work in the Loggia dei Lanzi), while the individual sculptures in the Piazza mostly date to the Renaissance, though of course copies have been put in place in most cases for preservation reasons. The great David by Michelangelo was moved to the Accademia in the late 19th century, though Cellini's bronze Perseus and other originals are still found outside.