The ampage, (data on common guitar tubes).
Andrea Ciuffoli, (6336C, PL504, EL509).
Duncan's Amp Pages' datasheet locator, (this page linkes all tube datasheets on the WWW, great stuff!).
Frank's Electron tube Pages (Lots of information a datasheets).
HongKong audio, (Data on many DHT's and other tubes).
Sub-miniature tube data, (data on "pencil" tubes).
Triode Electronics Inc., (Lot's of very complete sheets).