Staff, clefs, ledger lines: http://www.musictheory.net/lessons/html/id10_en.html
Learning Notes: http://www.musictheory.net/trainers/html/id82_en.html
Measures and time signatures: http://www.musictheory.net/lessons/html/id12_en.html
Rests: http://www.musictheory.net/lessons/html/id13_en.html
Note trainer: http://www.musictheory.net/lessons/html/id11_en.html
Brass trainer: http://www.musictheory.net/trainers/html/id86_en.html
Dotted notes and ties: http://www.musictheory.net/lessons/html/id14_en.html
Misc. Theory http://www.musictheory.halifax.ns.ca/lessons.html
Misc. Theory, geared more toward beginners. http://library.thinkquest.org/15413/theory/theory.htm
Wood Wind Fingering site. Includes alternate fingerings as well as trill fingerings. http://www.wfg.woodwind.org/index.html
Composers: Brief biographies of nearly 70 composers, which will bring to life the artists and their works. http://www.essentialsofmusic.com/composer/composers.html
Online music terminology glossary to include musical examples. http://www.essentialsofmusic.com/glossary/glossary.html
Music Eras: Overviews of the six main periods in music history -- Middle Ages, Renaissance, Baroque, Classical, Romantic and Twentieth Century. http://www.essentialsofmusic.com/eras/eras.html