Amps which are Great, but either Unknown or Underpriced

I'd vote for Audio Analogue great sound for not a lot of money.

AirTight ATM1. Can be run as an integrated with 2 inputs and you can use them later with a pre or phono pre. You also can add a second one for monos for driving big or unefficient speakers.
They sound gorgeous. Art Dudley's ref amp. I have pair of ATM 3 for over 20 years and only one trouble fo fix one one amp.

Vincent Audio. Designed in Germany, manufactured in China. I have pr. of SP-998 mono blocks. These compete with or surpass Power Amps costing many times there RRP of Aus.$6k. The fact I picked them up brand new for half that, make them a contender for one of the great bargains in audio history. 300W. into 8ohms. 50W of that Class A. these have the best grip on bass I have ever experienced and will embaress some of the overpriced big names costing truckloads more in musicality.

Havn't heard any of their  other Power Amps, but would like to try one of their Hybrids one day.

I have the SA -T8 Pre-Amp which is sublime and will beat much more expensive pre's. Also have the SA-T1 which is ok in a more budget set up if you pick one up discounted as I did.

Acoustic Imagery Atsah 500, 400 watts, 2K, awesome sound

Okay ... "little known and sounds great:" 

Years ago I bought a Dyna 120 in perfect condition at a garage sale for four dollars. I sent it back to Minnesota to Frank Van Alstine so he could install his circuits. What I got back was a 60 wpc giant killer. It was solid state but if left on for a few hours took on a sweetness all its own. The bass was killer too. Over the years, I've referred many people, especially those on a tight budget to the Van Alstines folks. Good people. Good electronics. Great prices.