Metronome by BestMetronome.com
Online Metronome - Keep a steady beat
Recordings of Standard of Excellence Book 1 & 2 - Play along with the lines in your lesson book.
Smart Music - a subscription based program that is like "Guitar Hero" for your band instrument - online assessments, thousands of solos, band songs, method books for every instrument and voice. Wonderful supplement to private lessons.
Chomatik - free play along with your favorite songs
Odogy.com - From games to learning tools, the goal of these applications is to motivate musicians, young and old.
Music Flash Cards - A great way to review note names.
Music Racer - Compete against other players to see who can name notes the fastest.
Music Dictionary - Find definition of every musical term.
Musictechteacher.net - tons of games and quizzes on learning note names, rhythms, instruments and key signatures.
Musictheory.net - Lessons and quizzes on note names, rhythms, chords, key signatures, ear training and so much more
Noteflight - online music composition. Free program to write your own music.