Man...I haven't listened to Zeppelin in the longest time.
1. No Quarter
2. Trampled Underfoot
3. Dazed and Confused
5. Achilles Last Stand
That's about it. And I must say, No Quarter is one of the greatest songs ever written.
I don't know, but The Song Remains the Same is definitely in there... So is the Rain Song, and Celebration Day. Maybe also Tangerine, Gallows Pole, That's the Way, and Your Time is Gonna Come. It's too hard for me to pick... You'd need to narrow it down to acoustic songs and electric, 'cause that's the only way I could actually make that list.