Cryostasis.
God.
The battle itself was meh, but it was fucking GOD.
I cant decide on just a single battle so…
Resident Evil 4: “IT”
Lost Planet 2: Giant Sand Akrid (hard to chose this game has many epic boss battles)
Half-life: Nihilanith
Twilight Princess: Ganon
Diablo 1 - fight with Diablo because, well, he’s diablo - The butcher, King Leoric, Warlord of Blood. D1 and not D2 because D1 bosses looked cooler and more dark.
Doom 1 - Cyber-demon boss fight & Spider Mastermind. Although the SM was
cheap as fuck with his 100% accuracy chaingun, like the FH sergeants in Doom 2 - but times 100
Duke Nukem 3D - The Cycloid Emperor - that boss fight was badass.
“It’s down to you and me, you one-eyed freak!”
Doom 3: Cyber Demon! i could only win by cheating:’(
https://www.youtube.com/watch?v=y9rnI7tMfiU&feature=related
Still haven’t played Twilight Princess. I’m sure that would be mah #1 though.
Otherwise my favorite was actually the ending of HL2 :3
So you like to fight spinning metal walls?
I thought i was the only one 
/sarcasm
i think the ending of Descent: Freespace – the great war was good
https://www.youtube.com/watch?v=rH1ehGk4E_0 it was an epic game!!
I normally don’t like boss battles, I prefer the way they’re handled in HL2, but if I have a least favorite boss battle, it’s Hades from GOW3. I sucked so much at that, it offered me to go to easy mode instead.
Which I kindly accepted.
Best get on that, son. You have two systems to play it on, you have no excuse.
Zelda: Link to the past
The vitreous battle
No kidding, I have a gamecube 
But the Gamestop here in town sells it still for at least $45.
Renegade’s Boss fight was HARD
https://www.youtube.com/watch?v=OKau6cPtMGI
EDIT: The reason he has 200 HP is cuz he was playing on EASY
Ep2’s epic strider battle in the forest
Amazon.com is an amazing website to go to, just so you know:
https://www.amazon.com/Legend-Zelda-Twilight-Princess-game-cube/dp/B0009UBR3A/ref=sr_1_2?s=videogames&ie=UTF8&qid=1292810376&sr=1-2
Demon’s souls Tower knight definitely.
I’m gonna say this even though I may get flamed. Just torrent the iso and play it on Dolphin emulator with a console controller. You just need an ok system, and it works out fine.
That’s how I did it =)
Cheater. That’s the extent of my flaming.
I don’t have a Gcube or Wii, and I wasn’t going to buy one of them just so I could play one game.
nah, emerald weapon was better
The boss at the end of Fable II, that guy was sooo hard to kill.