These were mentioned earlier in the thread, but here are some more pictures. The mid-century modern look of the Heathkit AA-21 integrated amplifier is really striking, especially when view from an angle. This was a very early solid state amplifier, note the word "transistor" on the front panel.
View attachment 1966294
View attachment 1966296
The AA-21, of course, looks very similar to the classic AA-100 tube amplifier that immediately preceded it.
View attachment 1966301