I've bought a few different times from these guys and they are great to deal with. Quick response to email and quick delivery.
http://www.radiotubesupply.com Home of "Dr. Roy"
A good place to go for exotic Triode tubes and amps (2A3's, 300b's, etc. - One tube I saw there is a mamoth 13" x 3" dia.)...
http://www.aydn.com AYDN Vacuum Tube Audio
-----------------
If your looking for someone to repair your tube gear, check out NOS Valves, near Flint, Michigan. Craig is a straight-forward guy who loves to talk audio and doesn't charge an arm and a leg for his work...
http://www.nosvalves.com/