I can't beleive I found the willpower to trudge through 20 pages of this.. I am tired, so I won't take any detours.
I agree with most bosses posted here, and I wish to add another game into the mix : Y's III on the SNES.
I might only be my young age at the time, but two bosses where pratically impossible for me at the time. The fire snake-dragon thing in some caves, and the last boss. I don't remember much, except that I have waisted a sizable chunk of my time on those two.. I think the fire boss is near the middle of the game, though...
Gah, me iz too tired to think anymore. I'm off to bed.