Planet Harmonica: Bilingual French e-zine offers detailed articles on playing techniques along with interviews and record reviews. Links to past issues

The Diatonic Harmonica Reference: More than 100 pages of tips, techniques, diagrams, pictures, sound clips, music theory, improvisation, mail order price comparisons. Useful for beginner and expert player alike

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