All of the discussion about Cardassians in the philosophy got me wondering what everyone's favorite races are, and if you have a favorite book(s) focusing on them.
For me it's, in no particular order:
Klingons (A Time for War, a Time For Peace, Left Hand of Dstiny, Art of the Impossible)
Cardassians (A Stitch in Time, Terok Nor, DS9 Relaunch)
Romulans (Serpent Among the Ruins, ENT: Relaunch)