i cant think of many off the top of my head...
ive always liked fighting the chocobo eater in FFX tho

my favourite tbh has got to be Alec Trevelyan on Goldeneye 007
Fighting him on the cradle is awesome, it can be fun to make it easy on 007 mode or on agent, but it is a good challenge on 00 agent.

The best thing is getting all the cheats and putting everyone on fast animation + all guns and turbo mode etc