Sounds like a fluff book is a good pick.
Sixth World Almanac - Good: Good overview of the Shadowrun timeline and history. Good for info on various locations. Bad: A few really bad editing mistakes with a couple sidebars.
Corporate Guide - Good: Good rundown on the AAA corps, the history, important key players in corporate settings, the various corporate cultures, etc. Bad: Not a ton of content for veterans and older players, but the shadowtalk was fun.
Vice - Good: Rundown on the major crime syndicates and larger gangs. Lot of plot seeds for GMs. Nice update since Tempo shook things up in the underworld.
Running Wild - Good: Mix of crunch and fluff on the animal kingdom, more crunch then fluff. Also goof info for Biodrones, Great Dragons, Infected, Techonocritters, Ghosts, and a few others.