Other
Music Theory First Aid for Struggling Students
This site provides music theory information on such topics as rhythm, intervals, scales, chords, etc. Also, there is a fine section which describes the basic concepts of form and structure.
Other
Using Different Time Signatures to Create Interest
When composing, it can help to add interest to your music by using time signature changes. This article touches on how to use different time signatures to give the music a little push in a new direction.