The Tube CAD Journal Great site with tube related info and articles
Radiomuseum Most comprehensive radio database on the net
DIY Audio forum and huge list of tube/audio related links
Thermionic.org very nice HAM-radio site, very cool GM100 project.
Triode Dick Another fellow dutch tube addict, great stuff!
DHT Rob Site with really excellent SE tube projects!!!!
RaymondAudio The title says it all
Frank Phillipse Truly magnificent site for european data sheets (I'm jealous), he has almost every tube listed!!!
Enjoy the Music by Steve Rochlin. Neat site with lots of info on audio and more...
SJS Electroacoustic Amp design info