Tube vendors.

As for me, Vintage Tube Services.

Vintage Tube Services for me.  Several purchases with reasonable prices and excellent tubes.  

I've dealt with Brett Jesse, Kevin Deal, Andy and Viva tubes on multiple 
occasions and have had great success.  I have also purchased 30 or 40 tubes from a local dealer in PHX that has been very good.  Dave at Arizona tube supply.  Very good.  I would say he seems to have mostly USA NOS tube brands, not so much on the European brands.  Great source.

I've bought many tubes from Brett Jesse and gotten great support.  He tends to focus mostly on obscure NOS (and expensive) tubes.

Recently I've bought quite a bit of tubes from the Tube Depot and have been very impressed with their service, selection, and prices.  The Tube Depot mostly focuses on new production tubes, so the prices are generally pretty attractive.

My vote is for Andy at Vintage Tube Services. Great stuff and reliability.