I love reading biographies. As a fan of the American founding era, I've found the following biographies of Founding Fathers to be particularly excellent. I'm not suggesting that these are the very best biographies written, nor am I saying that they are the most scholarly. But they are a great balance between solid scholarship and excellent readability. They are highly recommended.
1. The Autobiography of Benjamin Franklin by the man himself
There's nothing like reading primary source documents. The Autobiography of Benjamin Franklin remains an all-time great classic of American literary history.
2. John Adams by David McCullough
This Pulitzer Prize winner is one of the most comprehensive and absorbing biographies I've ever read. McCullough is unfairly looked down upon, because he lacks "proper" historian credentials. More evidence of the academic elitism that sadly permeates much of our culture. McCullough is a consummate researcher and a stickler for detail. His scholarship is solid. And he knows how to tap into the human element and tell a good (and accurate) story. I highly recommend McCullough and all his books, especially John Adams.
3. The First American: The Life and Times of Benjamin Franklin by H.W. Brands
Benjamin Franklin is one of the fascinating characters in world history, and certainly one of our most interesting Founding Fathers. H.W. Brands paints a vivid portrait of Franklin's life. I had a hard time putting this one down. Definitely worth your time.
4. Founding Father: Rediscovering George Washington by Richard Brookhiser
This is, by no means, a comprehensive biography of Washington. For that, check out Joseph Ellis' His Excellency (which I recommend with some qualifications) or James Thomas Flexner or Douglas Southall Freeman. However, Brookhiser does a superb job examining Washington's legacy in American popular memory. Very insightful and very interesting.
5. Alexander Hamilton, A Life by Willard Sterne Randall
I confess that I have not yet read Ron Chernow's very popular biography on Hamilton. If I had, I may recommend it, instead of Randall's. But, of the biographies on Hamilton which I've read, Randall's Alexander Hamilton is the superior one. I was swept up in the story of Hamiton's life. He is truly the rags-to-riches story of the American founding. In many ways, Hamilton epitomizes what it means to be an American more than any other Founding Father. Honorable mention goes to Richard Brookhiser's Alexander Hamilton, American.
While not a biography per se, I would also highly recommend Founding Brothers by Joseph Ellis. The book does a great job showing how the colorful characters of our founding era interacted to produce not only some of the most interesting dramatic episdoes in our history, but also the most successful nation the world has ever known.