Early
Diabolus in Musica: Guide to Early Instruments, Edinburgh University Collection of Historic Musica, Medieval and Renaissance Instruments, The Orpheon Foundation: Museum of Historical Music
Human Voice
National Center for Voice and Speech - Information, Questions/Answers About Voice Problems, Singing Voice, Young Singers Checklist - Laura Claycomb
Percussion
Build the World's Cheapest Drumset, Drumbone Construction 101, Drummers Forum, How to Make A Shekeré, Liewil's Djembe Pages, Llangybi & Usk Junior Bell Ringers, Mexican Maracas, Minor Strikerz, Percussion Instruments
Stringed
Guitar, Viola, Viola da Gamba, Violin, All Things Strings, Banjo Setup Webpages, Chris Peterson Hammered Dulcimer, Doghouse Slappers Society, How to Play the Mandolin, Jim Bottorff's Banjo Page, Making a Simple Lyre, Rebec Page, The Celtic Harp Page
Woodwind
Bagpipes, Bassoon, Clarinet, Crumhorn, Flute, Oboe, Recorder, Saxophone, Brother Steve's Tin-whistle Pages, Contrabass Compendium, How To Play the Jug, Jack's Harmonica Country, Making PVC Didgeridoos and Bamboo Didge Modificati, The Alphorn in Switzerland, The Classical Free-Reed, Inc., The Woodwind Fingering Guide
World Cultures
Audible Artworks: Selected African Musical Instrum, Celtic Music Instruments, Griots' Musical Instruments, Tibetan Musical Instruments, V. Mishalow - Folk Instruments of Ukraine, Vietnam Traditional Music - Musical Instruments
America's Shrine to Music Museum
Founded as an academic support unit of The University of South Dakota, this museum houses more than 10,000 instruments. Features virtual galleries with pictures of unusual, beautiful, and historic instruments from the collection.
Caramax Turtle
Kids can play games with Caramax Turtle and learn the sounds of musical instruments.
Instrument Encyclopedia
A guide to more than 140 musical instruments from all parts of the world. Includes photographs and descriptions.
Kidport Reference Library: Musical Instruments
Learn about the different instrument families and the individual instruments within them. Pictures available.
kidsregen.org Organic Music Archive
Learn to make various musical instruments from simple materials.
Learn about Instruments
Listen to samples and learn about different types of instruments.
Mudcat for Kids
Learn how to make musical instruments from everyday materials.
Music Match 'em
Game asks you to match various instruments to the sounds that they make. (Requires Flash.)
Wikipedia Listing - Musical Instrument
Encyclopedia entry includes descriptions of various classes of instruments and links to related topics.