I have found this book to be very helpful as I have explored classical music over the last seven years: "The Essential Cannon of Classical Music" by David Dubal.
http://www.amazon.com/Essential-Canon-Classical-Music/dp/0865476640/ref=sr_1_3/186-8494971-9735748?ie=UTF8&s=books&qid=1252613523&sr=1-3
http://www.amazon.com/Essential-Canon-Classical-Music/dp/0865476640/ref=sr_1_3/186-8494971-9735748?ie=UTF8&s=books&qid=1252613523&sr=1-3