Some hobbyists who are building their own tube synthesizers:
The most complete list of modular-synth form factors we know of. Covers both current production and defunct manufacturers.
Legend Music---support for Hammonds and other stuff.
Magnus Danielson's very good synthesizer hobbyist page.
A good place to start learning about analog synthesis.
One Electron--very good output transformers, plus one of the best libraries of classic
vacuum-tube circuit schematics on the web.
Wikipediocracy -- the focus of my rage. Because Wikipedia is crap.
This site has been online since November 1998.
Last update March 2013.