Amps which are Great, but either Unknown or Underpriced

Class D Audio SDS 470

Class D sounds grey to me.  Devialet sucks as well as Hegel...Highly regarded by some.

+1 for Monarchy Audio. I have a pair of sm70mkII's that sound beautiful. I believe them to be a huge value.

+1 Line Magnetic 518ia .... Or 219ia if your bank balance and back can manage it.

Though they've gotten several reviews in the last few years, I second Coda. They make really amazing stuff. No fancy bells and whistles--just clean, solid, no-nonsense engineering with terrific parts that work well together. 

I've owned several Coda amps over the years and currently own an S12.5, which drives my Jena Labs speakers very well. Really clean and super-transparent, with a touch of warmth that ties the whole package together. Lightning-fast but not overpowering bass as well. An acquaintance of mine has a 15.5 that powers a pair of Legacys, and that combo is magical too.

They're certainly not bargain basement in price, but for what they offer sonically, they're a fabulous value, IMO.