In the solid stae realm, all the Clayton Class A amps are great. The sweet spot is the Clayton M200 at MSRP $9,500 of 200 watts/channel of pure Class A goodness.
Next on the list would be the McCormack DNA-500 with a bit denser and more liquid sound. Not quite as accurate to the signal as the Clayton's, but it is still great.
The Modwright KWA-150's are also very good, as are their new KWA-100SE's at MSRP $3,995.
In the low-watt tube realm the Coincident Technologies Frankenstein's at 8 watt/channel amp is incredible. Paired with many high sensitivity speakers, such as Coincident's own Super Victory, Total Victory IV, and the Pure Reference will provide the listener with glorious sound.
Upping the tube wattage to 70 watts, Coincident Technologies Dragon mono amps are great. A great stereo tube amp is also the Einstein The Light in the Dark at 80 watts into 8 ohms and 115 watts into 4 ohms.