Of all the games you've ever played, what are some of your favourite bosses? I'm just wondering what makes a great boss, and what you think does.
Note: By boss, I'm not necessarily meaning an actual boss (EG: Nihilanth of Half-Life). I also mean stuff like final battles (EG: the striders and hunters at the end of Half-Life 2: Episode 2), mini-bosses (EG: Antlion Guards in Half-Life 2)... y'know, anything with enhanced difficulty, or requiring different tactics to the rest of the game, or... anyway, hope you understand what I mean.
Can't think of mine right now, but I'll put 'em up when I do.