These two coins from Thebes show the kind of shield that Thebans carried in battle, and on the other side one has a trident and a fish, for Poseidon, and the other has a drinking cup (Notice how both of the coins are struck a little off-center, because the striker was not being careful enough. Cheaters used to take advantage of that to clip off a little silver around the edges, and keep it for themselves.).
Eyewitness: Money (Eyewitness Books) (2000).
Sold!: The Origins of Money and Trade (Buried Worlds) (1994). School Library Journal says, “Grade 6-10-Covering primarily the ancient Mediterranean civilizations, this well-written, beautifully illustrated account describes early forms of money, how the first coins were made, and what they reveal to archaeologists about the people who used them.”
Ancient History from Coins, by C. J. Howgego (1995). Not so easy to read, but a good introduction to what we can learn about history from coins.
Greek Coins, by Ian Carradice (1995). This handbook for beginners shows some of the different types of Greek coins, with a little historical background. About a page per century.