Overblows:

Levyland - Howard Levy's articles on technique.

Overblow Players:

Howard Levy

Otavio Castro
Carlos Del Junco
Lengyel Attila

Adam Gussow
Jason Ricci
Frederic Yonnet
Roland van Straaten

Tinus

Harmonicas:

Seydell

Harponline
Antony Danecker
Filisko, Sleigh and Gordon
G.
Turboharp
Tony Ramos
Pearl

Harmonica Maintenance:

Pat Missin

Music Theory:

Aebersold
The Grotch scalefinder