Pretty basic topic. Which are your favorite boss battles? You don't need to detail your post if you don't want to, but here's my top 5:

5. Klungo - Banjo-Tooie

How can you forget about these hilarious recurring battles? This poor guy got more beaten up by his mistress each time he failed to defeat Banjo, yet somehow got stronger each battle. Already forgot? That's too bad.

4. Tartarous - Halo 2

As we all know, boss battles aren't too common in the Halo universe. This guy on the other hand made quite an impact as an extremely overpowered brute, willing to do anything to stop the Arbiter from deactivating the ring... even jump off the platform just to respawn again... A cheap battle, yes, but also very memorable.

3. Meta Ridley - Metroid Prime series

This bird-dinosaur resembling little fucker just wouldn't die no matter what Samus tried to do. You think lasers, 800 metres fall followed by an explosion would be enough to stop him? Nope. Two games later in the series and he rose again to battle Samus, while everyone tried to sew their jaws back on.

2. Ganondorf - The Legend of Zelda: Ocarina of Time

Oh, come on, it had to be here! What better way is there to finish off one of gamings most epic adventures but a ping pong battle till death, huh? I sure can't think of any... Except maybe cutting off the tail from an enormous pig!!

1. The Great Mighty Poo - Conker's Bad Fur Day

This opera-singing piece of shit would change everyones view on boss battles forever. Can you deal with the epic-ness?

Either the final battle with Kefka in FF6 because, even though he's a total pushover if you're overleveled (I invariably am), all the monsters preceding him are pretty awesome and "Dancing Mad" is beyond amazing and the whole thing remains one of the coolest things I've ever seen in a video game, or the decisive battle with Peace Walker (from MGS: PW, durrr) because it feels so apocalyptic but the female voice talking shit the whole time ("Bring it on!") makes it rather hilarious as well.

God of War III

- Poseidon
- Hades
- Cronos
- Zeus

God of War II

- Coloss of Rhodes
- Sisters of Fate

Of course there are other boss battles that I like or even love as well, but I'm a bit too lazy atm :P

Favorite:

Ornstein and Smough (Solo, not no online cheating BS) - Dark Soul's

Memorable:

Snake vs Ocelot - MGS4

I felt like the king of the world when I beat this, obviously with a bit of help but I did most of the heavy lifting myself.

And using the tonfas to do it makes you feel even better. That isn't me BTW. Those 2 are incredible.

Kefka - FFVI

Magus - Chrono Trigger

Ganondorf/Ganon - Zelda TP

Meta-Ridley - Metroid Prime

Psycho Mantis - Metal Gear Solid

Hydra - God of War

Sinistral 1-4 in Lufia II

oh and should totally hit myself for forgeting:

Luca Blight in Suikoden II

.

Resident Evil - Tyrant
Resident Evil 2 - Birkin (all forms)
Resident Evil 3 - Nemesis (all of them)
Resident Evil 4 - El Gigante + Krauser
Metal Gear Solid - Sniper Wolf + Vulcan Raven
Metal Gear Solid 2 - Hydra Jet
Metal Gear Solid 3 - The End + The Boss
Final Fantasy VII - The weapons + Safer Sephiroth
Final Fantasy X - Jecht + Sin
Final Fantasy XIII - The Proudclad
Crisis Core: Final Fantasy VII - Genesis + Sephiroth
Skyrim - Dragons
Tales of Vesperia - Alexei + Gattuso
Fallout 3 - Super Mutant Behemoths

Can't think of any more, the best would have to be Nemesis for me though.

It's too hard to make top list, most of my favourite boss battles were from Metroid, Metal Gear and Resident Evil series.

But, If I have to pick a sigle game for the best boss battles it's definetly Alien Soldier.

(Oh yes. and The Great Mighty Poo would also be in my top 10)