Other
Islandnet.com: The Gottfried Silbermann Legacy
Excellent site describing Silbermann's work on the organ as well as the development of the piano. Many interesting links to musical societies which also have musical worth.
PBS
Classics for Kids: Musical Instruments
An A-to-Z directory of all the instruments and tools of the orchestra. Each entry includes a description, a picture, and a sound sample.
Other
What Are Historical Keyboard Instruments
Provides information about historical keyboard instruments such as the clavichord, harpsichord, fortepiano and organ.