Music Theory
Music theory.net: Steps and Accidentals
Provides an explanation of half steps, whole steps, flats, and sharps. Illustrated examples accompany these definitions.
Music Theory
Music theory.net: The Minor Scales
Listen and learn with this explanation of minor scales. Each description of harmonic, melodic, and minor scales provides an illustrated example, and audio clips.
Other
The Basics of Reading Music
This site is an overview of how to read music. The basics of notation such as note and rest values, the names of lines and spaces of both treble and bass clefs, etc. are covered. Includes downloadable audio files.
Other
Ruby Cliff Computing: Elements of Music Notation
Fine site that focuses on music notation and on learning how to read it with a focus on the guitar. Includes charts, tips, and other useful information.
Other
Teoria: Key Signatures
This site from Teoria's Books offers a short, easy to read article on Key Signatures. An interactive keyboard makes the learning more fun.