Mmmm... when I pick up a classic guitar:
The Ballad (Testament)
Fade to Black
Stairway to Heaven
But, when I'm drunk and at some party, usually they gave me a guitar and we start to jam on a little blues a friend of mine write, called "Pistone" (Piston), just for fun (it's basically the same riff over and over, with words about harleys and bikers, and improvised-bluesy solos). Oh, and when I'm drunk every punk song is f****n' good to play too.
Oh, there's also Led Zeppelin's Rock'n'Roll!!!