What great statue was Michelangelo commissioned to create for Florence? http://www.michelangelo.com/buon/bio-index2.html
I believe that the answer that you are looking for can be found in the "Early Years" section of the site that you have provided a link for. The answer is down toward the very bottom of the page. The great statue that Michelangelo was commissioned to create for the city/state of Florence was his famous statue of King David from the Bible.
The statue of David is, to this day, seen as one of Michelangelo's greatest works. According to the michelangelo.com link, the statue is one of the high points of his career and was meant to express his feelings about the republican form of government that had sprung up in Florence.