Game: Street Fighter II Turbo
Boss: Akuma

The very first time Akuma showed up, that was pretty amazing..........then you just learn to smurfing hate him over the decades.

Game: R-Type
Boss: Dobkeratops (several other names)

Probably as famous as the series itself. I think it makes an appearance in some way in every game?

Game: Doom
Boss: Cyberdemon

"A missile-launching skyscraper with goat legs. 'Nuff said."

Game: MGS 3
Boss: The End

The series is known for it's creative characters and bosses, but The End is probably my favorite just for the numerous different ways you can interact with him or change how the fight plays out. You have more than one way of avoiding the fight altogether. Runner-up is fighting The Boss just because of the feels.

Game: Ridge Racer 4
Boss(es): Assoluto Volcano, Age Solo, Terrazi Utopia, Lizard Nightmare, and Pac-Man

The Ridge Racer games have always had fun little boss cars to unlock, and while Rage Racer might be my favorite in the series, I think 4 has the best boss cars. The Rocket Car and Pac_man always made me smile.

Bonus Boss I think I'd like.

Game: Mega Man 9
Boss: Splash Woman

So, the 9th installment gets a nod from me for simultaneously trying to make a game in the tradition of the early games in the series, while changing it up by finally introducing the first (and only?) female boss in the series.