I recently read and highly recommend this book by Mark Kurlansky to anyone interested in salt or world history. It's a fun and interesting romp through the ages, following salt from ancient history to the present. It's written as a popular non-academic history and, as such, is a pretty quick read for the beach or whatever vacation you're on. I thought his most interesting chapters were on salt in the ancient world and how important it was in the transition to a merchant economy.
The strength of the book is that is uses salt as a mechanism to explore interesting stories and personalities from around history. Kurlansky does not view the world through a lens of salt (i.e., treating all events as revolving around salt), but rather, uses salt as a means to explore history. Good stuff.