I like all Zep songs but I'll nominate 1 or 2 from each album that deserve more recognition:
Babe I'm Gonna Leave You / How Many More Times
What is and What Should Never Be / Bring it on Home
Gallows Pole / Since I've Been Loving You
Four Sticks / When the Levee Breaks
Over The Hills and Far Away / The Crunge
In My Time of Dying / In The Light / The Wanton Song
All of Presence, especially For Your Life
In The Evening / Hot Dog
Poor Tom / Ozone Baby / Hey Hey What Can I Do