If this is in the wrong forum, I apologize in advance, but what exactly is a tube amp? I've heard of them yet I dont not know what they might be. Not to sound like a dunce of the guitar world, but is it special sound it makes that gives it it's name? Or a certain feature that it is made with?
to the above poster's response... don't bother with that thread until you actually look at what brand to get, because that's all it will tell you.
It is the way they are built. They use vacuum tubes to shape and amplify the sound as opposed to solid state amps that use IC chips and do not use vacuum tubes. Generally people prefer them because of their nicer/warmer tone than solid state amps. The tubes cause the amp to distort much more smoother so it sounds much much better.

For a broad(not just instrument amplification) overview on what they are check out this(they are also referred to as Valve amplifiers).
2004 Fender American HSS Strat
Hughes And Kettner Switchblade
Schecter C-1 Hellraiser FR
Epi LP Classic
Epi G-400
Yamaha acoustic
Boss DD-3 Delay
B.Y.O.C. MXR Distortion+
Vox Wah
Ibanez TS9 Tube Screamer