Turrican 2, one my all time faves has to be a main contender. There are so many great games from that era and console that a list would confuzzle you so I’ll just keep it sweet and simple with that one choice…for now ;)
Good choice freezebug, i would have suggested one of the Turrican games too – really wish someone could revive that IP.
Also Bubble Bobble, Rainbow Islands, Stardust (forerunner to SuperStardust), The Chaos Engine, Smash TV, Arkanoid (excellent Breakout clone), Fire & Ice (great platformer), just to name a few more. (I haven’t checked that these are all available on site above).
If you haven’t played Amiga games before gazza just bear in mind these are old games and might not have the same appeal as they have for oldies like me! ;-)