The Quad 22 series is a classic, as is the 405 power amp released in the 70s (It was also used in professional studios which is always a good sign) and the way it operated seems to be the forerunner of Class G, after that the NAD 3020 rewrote the rule book for budget amps causing all the other manufactures to go scrabbling to their R& D dept. to try and get something to compete, and the Lecson was the start of the super amp generation.
After the above there is not anything of note as a number of manufactures started engineering a house sound into their products, and the rest just refined what was already there. (The development of Class D & Class G amps was a step change but are used mainly in AV)
Bill