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.
Stanford University
Ccrma: Common Music Notation
This resource features information on notes, rests and many, many other basic music theory examples.
Other
Piano Music Sight Reading Practice
Actually this clever site drills pianists on note names and note placement on the keyboard. Kids can access this site at home for practice. Both treble and bass clef are used.