+1 I've dealt with both Doug and Mike at KCA and both are excellent. I've also bought from Brent Jessie and Antique Electronics Supply with success. Brent gets some cool tubes in sometimes that are off the beaten path.
I bought from Eurotubes a couple of years ago. Knowledgeable staff, great prices and fast shipping, but they only sell one brand of tubes so it's pretty much a one-size-fits-all approach.
Last year I bought from The Tube Store. Similar experience but a wide variety of brands both NOS and current production, perfect matching using the actual plate current draw. Located in Canada so no cross-border hassle for me. I will buy from them again the next time I need tubes.