The Franklin D. Roosevelt Presidential Library and Museum, located at the site of FDR's house in Hyde Park, New York. The website has an online museum, lots of historical documents, and a short biography and timelines of FDR's and Eleanor's lives.
The Franklin and Eleanor Roosevelt Institute (also located at FDR's Hyde Park house) has tons of historical documents and resources for students and teachers.
Back in 1994, PBS did a biography on FDR as part of its American Experience series. The website for the show contains a wealth of information, including a biography (focusing on his political career) and primary source documents.
In 2000, Time magazine named FDR as one of two runners-up for person of the century (the other was Gandhi; Einstein won the prize). This colorful article by presidential historian Doris Kearns Goodwin makes the case for his impact on the country and the world.
The White House has a short, official White House biography of FDR. White House
The White House also have a second biography in their "For Kids" site: