As much as I like some of the other platformers mentioned here...
I have to go with Superfrog as the all time best Amiga platformer. It has Eric Schwartz movies, great graphics, catchy tunes, great level design, fast scrolling, great animation, a fun little green gloppy thing to throw around, a good difficulty balance, those bouncy springboards that cause massive frog abuse in the later levels, and, of course, the icy and slippery slides. Just hearing the frog screaming WEEEEEEEEEEEEEE as he zings headlong down the hill at about 1,000 mph still cracks me up!
Another great platformer that I didn't see mentioned so far was Fury of the Furries. I love the little dude that swings on the ninja ropes! :-)