1. "Alfred Basic Piano Library" series by Willard Palmer and Amanda Lethco. This series emphasizes finger-position playing.
2. The Suzuki Piano School, by Dr. Shinichi Suzuki. The Suzuki approach emphasizes ear training and the production of beautiful tones on the piano.
3. "The Music Trees" series, by Frances Clark and Sam Holland. This series emphasizes music reading.
4. The "Piano Adventures" series, by Nancy and Randall Faber. This series empahsizes good pianistic technique.
5. Lily Yeh's own teaching materials.