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Drum Bum: A Drum Lessons Database
Providing "Over 400 free Lessons and Tabs," this resource includes learning ideas and information for everyone from the drum novice to the expert. In addition to including lessons on a wide range of instruments, this resource includes...
Wikimedia
Wikipedia: Percussion
A basic article on percussion instruments lists several examples of percussion instruments, provides a distinction between membranophones and idiophones, and lists instruments that are tuned vs. ones that are not.