[Jazzman53]

I think a Bob Carver design deserves to be on the list too.  His Lightstar and Silver Seven amps come to mind but, in terms of impact, my choice would be the M1.0t.... which is the amp that won Stereophile Magazine's "Carver Challenge"-- going toe-to-toe with a Conrad Johnson Premier Five tube amp. 
 
For some reason I'm unable to attach a link here to the Sterophile Magazine article but it's easy to find on a Google search if anyone is interested.   

[ec]

In addition to the 4B some of these amps should have been mentioned:

Quad II monoblocks
Jadis - take your pick
Adcom GFA-555
Sonic T amp

[John Casler]

Seriously the most significant amp for me and it solidified me and my passion for all things audio was the Dynaco 400 amplifier

James

No doubt, a significant amp and I think its primary design was from my old buddy James Bongiorno.

Someone also mentioned Bob Carver, and he really ramped up with the Phase Linear 400 and 700 models and singlehandedly started some of the really "HIGH POWER" amps we see today.  While they were not truly audiophile amps, they did move higher power amps into the mainstream of High End.

[poseidonsvoice]

The first time I heard a Nelson Pass Aleph 3 in 1997 was a pretty mind blowing experience for a budding young audiophile.

Another mind blowing experience was listening to the Atmasphere M60 for the 1st time.

Both of these designs I believe changed the amplifier paradigm each in their own way (solid state and tube).

Anand.

[vegasdave]

At the risk of upsetting some of you, I'm not a fan of Carver's work. I've listened to it, and found it rather unmusical.

[lanchile]

I had a Marantz 2238B, it was over 25 years old and it was fantastic. never gave me a single problem and kept going and going...I gave it to my brother in law and it is still working 100%.The new Marantz now are just Crab!!!