Understanding Musical Form
http://yourpage.blazenet.net/rsmusic/composition_children_with_skills.html#anchor_musical_form
This site provides a brief description of several musical forms, such as AB, ABA, Theme and Variation, Rondo, and Sonata.

Index to Form
http://jan.ucc.nau.edu/~krr2/index_form.html
This site provides a brief text-based description of essential concepts related to musical form.

Classical Music Pages Musical Forms Index
http://w3.rz-berlin.mpg.de/cmp/musical_forms.html
This on line index provides descriptions of important musical forms in music history. Hyperlinks to biographies of important composers with related forms and genres are also included with each description.