Just 3 of my favorite game bosses (Yes, they are all from the same game)
(Skip to 20 seconds in to skip the intro)
Gohma
I just find grappling onto a dragon's tail to be pretty awesome (I will never understand how a game made 10 years ago could withhold so many particles)
Helmaroc King
Run away from rising water, then fight on castletop arena over ocean.
Molgera
Fight on sand that shifts during battle against a giant flying centipede.