I love Led Zep but my favorite songs are their live stuff. I like their studio songs, but their live songs are just a step above IMHO. They really captured something special on the The Song Remains the Same, so all my favorites come off that film.
BTW- I saw them live in '95 in McNichols in Denver. Damn good show.
In no particular order from The Song Remains the Same:
Since I Been Loving You
Dazed and Confused
Stairway to Heaven