SPAH.org is but one of many sites on the internet dedicated to the harmonica. There are of course harmonica manufacturers, retailers, customizers, and educational publishers online, but perhaps just as importantly there are a number of places where harmonica players from around the world can talk to each other. The list below includes sites that do some or all of these things. It is by no means comprehensive and will continue to grow and change as the online harmonica community grows and changes.
Modern Blues Harmonica: Founded by blues harp legend, writer and scholar Adam Gussow, Modern Blues Harmonica is dedicated to getting you to play the blues. Gussow offers instructional videos, harp tab, gear and listening recommendations and a forum. Gussow also runs his own music label, with a roster that includes himself and one-man-band Brandon Bailey.
Slidemeister: The internet's self-described "Chromatic Oasis," which should say it all. Slidemeister is a chromatic-centered community with an active discussion forum. Topics do range from diatonics to current events, but the focus of the forums is squarely on discussion of the chromatic harmonica.
Harptalk: Harptalk is a discussion board powered by Yahoo!Groups and sponsored by harmonica retailer Coast2Coast Music. Its stated purpose is to "discuss harmonicas, harmonica playing, and harmonica related equipment, as well as to share tips, techniques, and experiences."
Harp-L: Started in 1992, Harp-L is the internet's oldest harmonica message board. In its time it has covered all aspects of harmonica discussion. The site has a complete searchable archive, and more current posts can be viewed on their Yahoo!Groups page.
JazzHarmonica.org: Created by jazz chromatic player Wim Dijkgraaf, jazzharmonica.org is mainly an educational site aimed at teaching people how to play jazz on the chromatic with a focus on inspiring improvisation. The site offers free articles, mp3s, videos and a discussion forum, as well as paid video-conferencing lessons with Wim himself.
BluesHarmonica.com: David Barrett, famous for his Harmonica Masterclass series, fills this website with educational videos, mp3s, lesson plans and interviews. The site also has contests and forums staffed with well known harmonica players serving as "forum experts".
If you know of a site that should be listed here but isn't yet, please tell us about it.