I just finished reading Simon Singh's "The Code Book." It covers the history of cryptography from Mary Queen of Scots to modern encryption that is used to ensure the security of things such as online shopping. While the book does talk a little about the math of cryptography, the non-math reader should have no problem following along. Singh does an excellent job of explaining, in clear terms, how the codes worked -- and how they were broken. Singh also tackles some archaeology -- code-breaking and deciphering long-dead writing have common attributes.

I got the book for $4 in the bargain books at my local Barnes & Noble. So, check there first, otherwise, you can use the link above to buy it from Amazon.com.