I would suggest going to
www.GameRoomAntiques.com or
www.crowriver.com
The book that I would recommend that is currently in print is the Fey book "Slot Machines, the first 100 years"
The best set of books that I have ever read are the 100 most collectible series by Dick Bueschell. There are 4 books in the series and they are great reading. I think these are out of print but I think Ken Durham at
www.GameRoomAntiques.com might have them.
If you want to read some old reviews then check out
http://www.ibuyoldslots.com/COCD/index.htm Once there click on articles and then click on all articles by Ken Durham. He has a good article which discusses the different books. The article is old but since very few books have come out recently it is still valid.
As long as I am plugging "Coin Op on CD"
you might check out all the different areas of it at
http://www.ibuyoldslots.com/COCD/index.html you will find hundreds of photos and even videos of some pretty rare machines. Do not attempt the videos if you are on dial up (they are pretty large files).
Dave