Kinderbach. As a member of the TOS Homeschool Crew I was given a 3-month membership. Since it was designed for children much younger than my own I was not able to actually use it to form an opinion on how effective it is. However, it is very visually appealing, offers really great support, and looks like a lot of fun!
To use the program, you will need a computer and an electronic keyboard or piano. You do not have to have any musical training yourself. The online lessons are $19.99 a month or $95.88 a year. Alternatively, you can purchase the piano lessons on DVD for $40.45 per level. There are 6 levels. Each DVD package includes an activity DVD, a music audio CD, and an activity book CD (with printable books in PDF format). If this sounds like something you might be interested in, check out Kinderbach's website for free online lessons, sample e-books, coloring pages, and song download.