1. Gears of War 3 - Myrrah Final Boss Fight
It's got suspense, tactics, and when you finally win you're like "**** yeah! take that witch!"
2. Wind Waker - Ganon Final Boss Battle.
The finished is just so awesome, pictures can't even capture the awesomeness.

3. Metal Gear Solid 4 - Meryl Silverburgh Wearing a Wedding Dress
This was my favorite part of the entire game, that dress really accentuated her curvaceous arms and upper back. ^^
4. Blue Dragon - Zola Turns
At the second part of the final boss fight, you learn that Zola was given a part of Nene's soul and that she was working for him. But it turns out as she was traveling with Kluke and co, she learned that she had the power inside her all along and when he goes to get his spirit back, she had cast it aside.
5. Final Fantasy XII - Yiazmat
Boasting 50 Million+ HP, you're in the fight of your life with this one.
Some people ran away and came back to fight Yiazmat... Well, I took down all 50 million in one go. And people were saying it took them hours to do it, I think one person posted 4 hours... I defeated him in a measley 30 minutes. The entire game took me between 111 and 132 hours, forget exactly how long, to do everything.