Have a favorite, cheap tube? You're welcome to post about it!
Another gem: The 6AQ5.
As far as the large RF tubes go, I suggest the 811.
Like BIG triodes? There you go- triode power on the cheap. Filament draw is 6.3 volts @ 4 amps. Not too bad! Plate dissipation is only 45 watts, but that's still enough to make a decent SET or a powerful P-P amp.