The Diatonic Harmonica Reference:Reference includes tips for blues harp, techniques, music theory, improvisation, overblows, gapping, tuning, prices, and tab. Over 50 pages of tips and techniques.
Harmonica Note Layout Program: Javascript program lets you specify harp and/or music key, position, or scale type. Determines harp; note layout is displayed with the notes in the scale highlighted. Other options available.