WEll, that's a tough one since there are a LOT of games with pathetic final bosses, all with obvious weak points. For me, I'd have to say:

Castlevania SotN's Dracula:
Just use a Crissagrim and he's finished in less than a minute.

FF4's Zeromus:
PATHETIC. Just throw Excaliburs at him, and he's DEAD.

FF5's Neo Exdeath:
4 Samurais with Coin Toss

FF6's Kefka:
1. Genji Glove+Offering+Illumina+Atma Weapon=kill
2. Gem Box+Economizer+Quick+Ultima=kill

FF7's Bizarro, Safer Sephiroth:
Knights of the Round

FF8's Ultimecia:
Squall's Renzokuken and Lionheart

Grandia's Gaia:
Just use regular attacks

FFT's Altema:
T.G Cid, need I say more?

Secret of Mana's Dark Lich and Mana Beast:
Lucient Beam Lv. 9 and Mana Magic

Secret of Evermore's Cartron:
Gah, I'm not even gonna explain how.

Lufia 2's Sinistrals:
Diddo on this one

The final boss for every Zelda game
The final bosses in all three Soul Blader games

The BEST final bosses have to be:

Chaos from FF1
Indalecio on Universe mode with his limiter off in Star Ocean 2
Genocide Heart from SaGa Frontier
Dark Ring from SaGa Frontier
Diva from SaGa Frontier
Charm Lord Orlogue from SaGa Frontier
Spriggian from SaGa Frontier
The Devil from SaGa Frontier
Boss Cross from SaGa Frontier
Deus from Xenogears
HAHAHAHAHA!!! Don't make me laugh... I could crush you like an insect. Heh heh, but first, I will tell you a breathtaking secret about the Angel's power... And the legendary force that was forged with it...

Rufus Shinra