I was going to buy an Amiga the second that I saw it released at the Australian PC show... What made it from a 'want' to 'need - must have!' was when I first saw Defender of the Crown.
Games that continued to solidify the Ami's place as the premier graphics game machine during it's history:
FA-18 Inteceptor - made my RAAF Pilot brother sell his PC and buy an Amiga.
Lemmings - taking puzzle games to the next level
Populous - Taking strategy games to the next level
As far as 'full on screens of electric death' go -- for their day:
Silkwork (original)
Uridium 2