I got Led Zeppelin: All the Songs: The Story Behind Every Track by Jean-Michel Guesdon and Philippe Margotin a few months ago at Barnes & Noble, I'm just getting around to reading it now. Seems good so far
For me it was Dazed and Confused, easily. Although Communication Breakdown helped. I had heard a handful of Led Zep songs before checking out their first album (as everyone has), but the OG album definitely solidified me as a fan.