I haven't added anything to this thread in a while, but my favorite tubes right now are (at least they are parked in my amp for the past 6 months)
Amperex 6AM6 EF91
I wonder if these are the same as the famed Bugle Boys? I mainly like them for the extra soundstage (EF91 are all wide) and neutral presentation which works well with the HD650s.
I just search for these tubes on e-bay. I'm not sure where I got them but i surely did not pay more than 12 bucks for one of these tubes. Unless you have no problem spending lots of money (then why would you buy this amp?) then don't buy a tube advertised for the Little Dot. These are all standard tubes and there should still be thousands available out in the wild - but some are getting rarer, like the Amperex. However, there are lots of rebranded tubes (British tubes for the US) for cheap and you may get lucky.
Edited by Max F - 7/8/12 at 6:30pm