THEORY BASICS
Identification of notes, intervals, chords and scales: http://www.musictheory.net/exercises
Identification of key signatures: http://www.musictheory.net/exercises/keysig
EAR TRAINING AND INTERVAL RECOGNITION
Ear training and interval exercises: http://www.good-ear.com/
RHYTHMIC AND MELODIC SIGHT READING
Rhythmic Sight Reading: http://www.practicesightreading.com/
Melodic Sight Reading: http://www.practicespot.com/sightreading.phtml
Melodic Sight Reading: http://www.ronniesanders.net/free_sight-reading_music
Melodic Sight Reading: http://www.lightandmatter.com/sight/sight.html