What kind of book are you looking for?
If you are looking for a reference book to look up specific IDs of coins,
CNG's _Handbook of Greek Coins_ series is probably a
good choice. I don’t use those books because I prefer to look up common coins online and need specialized books for
rare coins.
If you want something cool to impress people you can’t go wrong with Folio-sized SNGs like
SNG Copenhagen or
SNG von Aulock. Most people have never seen folio-sized books and just pulling them off your shelf and casually flipping through them can be a treat.
I used to recommend Dennis
Kroh’s _Ancient Coin Reference Reviews_. 20 years ago it was a great way to learn what books cover the coins you are interested in. Sadly it is now 30 years out-of-date and copies are on offer on Amazon for $700!
If you want to become a top expert the books the
ANS recommends to graduate students wishing to learn
numismatics are given at
http://numismatics.org/seminar/readings/ . There is a PDF list of the classic works on
Greek coins.
I like books that can actually be read. I read _History Numorum cover-to-cover, but that isn’t the place to start. I recommend Frank
Holt’s _Alexander the Great and the Mystery of the
Elephant Medallions_. It has a hokey,
Hardy Boys-style title, but you’ll learn a lot about coins and the Bactrians.