yami (all 5 forms) from okami. man he was annoying but amazing boss at the same time
Ah yes, Ultemicia is damn hard.
final fantasy X end boss, seriously he looks as if he regularly eats other bosses as starters…
either kingdom hearts Sephiroth battle on hard mode…
The vizier from Prince of Persia: the two thrones
The final boss from Shadow of the Colossus is definitely high on my list. Also the boss of Arbiter’s Grounds from Twilight Princess (freakin’ Skeleton Dragon! The best boss of the game, definitely!) and the boss of GTA4 is fun for the drama factor.
I also beat Dungeon Siege 2 the other day which, by itself, may not be that awesome of ab oss fight, but I want listening to Our Solemn Hour by Within Temptation, and it really spruced it up.
And, of course, Ganon in The Wind Waker. To this day, one of them most emotional, dramatic boss fights ever conceived.
Honestly, in so many pages I’m surprised Shadow of the Colossus hasn’t already been mentioned. Every awesome boss fight ever packed into one game 
EDIT: Also, mention of T2T seems to be popular, but I thought that boss battle was drawn-out and frustrating (and I love the PoP series). I mean, it was just one long, crazy quicktime event with some rock-dodging thrown in…
Shadows of the Colossus is an obvious choice for Epic boss battles. That’s the only type of battle it has.
Legend of Zelda Twilight Princess was also one of the most epic Ganon battles I’ve played. Wind Waker was good, but the use of puppetry rather cheapened the entire experience. Twilight Princess gives you the magic duel, the monster duel, the horseback duel, and then the mano-a-mano duel to wrap things up. Very satisfying.
The Fire Dragon at the end of Fire Emblem url=‘https://www.youtube.com/watch?v=Q_1j2R2JaWA’[/url]
GlaDOS for the absurd commentary she gives
The last bosses in Final Fantasy 4, 7, 8 (10 was pathetically easy(the old zombie trick), and looked like a fat spider). Additionally the first battle with Rubicante (the guy in my avatar) in Final Fantasy four was awesomes.
My favourite one ever, however, is probably Andross from Starwing on the SNES (Starfox in the US), simply becuase he was the first game boss I ever defeated.
It took me almost an hour to beat the Twilight Princess boss because I didn’t want to hit Zelda. That was just a cheap shot, Nintendo 
I don’t really count that puppet battle as part of the real Ganon battle in WW, since it’s before Ganon’s monologue. I like to think of it as an independent miniboss
That floating head with the giant hands used to freak me out.
God damn, Descent was a great game. Somebody needs to remake that shit, like, in CryEngine or something.
Dude, I forgot about Descent! That game rocks! I gotta find me a new copy…
Did you mean this one?
Cos I meant this one: 
Additionally, I revoke ALL my earlier answers, and replace them with this:
Okay, the game may not have lived up to the rest of the series, but this battle is pretty damn epic: https://www.youtube.com/watch?v=v–J_4IBfMw
Gotta love giant bosses.
https://www.youtube.com/watch?v=qB7gj3kN3jc
Cave Story was just awesome.
Also
https://www.youtube.com/watch?v=qbT1cAsZ1UA&feature=related
was pretty damn epic. :jizz:
Seymour Omnis from FFX, the music is just too damn epic and it was challenging enough
Pkmn Trainer Red (Ash) from Pokemon G/S/C
Every boss battle in every MGS excluding (Mgs3) The Fear and the End :’(
Eldrith from Baldur’s Gate Dark Alliance (PS2)
Sarevok from Baldur’s gate (PC)
GlaDOS from Portal, main reason is GlaDOS being so funny I almost shat myself
Jon from Baldur’s Gate 2 (PC)
The last boss on Shadow Of The Colossus.
Absolutely loved that.
Diablo 2’s boss fights were amazing. Diablo, Mephisto, and Baal were all very fun, challenging, and a bit frightening.
For Me its gotta be Frank Horigan from fallout 2, looking back if you know the tricks its pretty easliy done, but if you didnt it was fairly hard.
But back in the day I felt I was getting som seriose pay back, sad I know but the joys of a young mind.
This isn’t really my favorite, but I loved Fontaine in Bioshock. Sure, he was easy, but it’s still very intense.