Very extensive list of various types of tube information including electronics humor section.
http://w1.871.telia.com/~u87127076/index.htm
A service from TDP with links to and information about the manufacturers, rebuilders and distributors/suppliers of tubes. An extensive list of data sheet sources.
http://www.tube.be
The site has some technical data including a reprint of the old text The Care And Feeding Of Power Grid Tubes which used to be given away by Eimac.
http://www.cpii.com/eimac/index.html
A scope clock, and tiny scope museum. The "Scope Clock" kit may be purchased.
http://www.cathodecorner.com/
Data for electron tubes from Berlin in Germany available in both English and Deutsch.
http://www.ginko.de/user/franz.hamberger/#tubes
Data sheets, search, history, tube bases, and numbering systems, substitution list and an extensive link list. All you would need to know about vacuum tubes.
http://home.planet.nl/~frank.philipse/frank/frank.html
Handy list of transmitters, transceivers and amplifiers and listings for which tubes are used in their final stages for RF amplification and modulation.
http://www.muchstuff.com/xmttube2.htm
Application notes on the care and feeding of Svetlana tubes, mostly for high power service.
http://www.rfparts.com/tubesvet.html#svetlana