What Are The "Must Have" Numismatic Books Nowadays

Depends on what you are collecting.
Basic books:

American: I Use U.S. Coin Digest.

World: Krause World coins, back as far as your interests extend,
Ancients: Sear's 1988 reprint, (Roman Coins) Byzantine Greek (two volumes) Roman Coloinal,
Medieval coins: 'Coins of Medieval Europe' by Grierson
Canadian: Charlton
Fake detection: 'Numismatic Forgery', by Charles M. Larson.
British: Coin Yearbook, Ancient Britain coins: Mack.
Medieval French coinage: Mayhew.
Australian: Rennicks or Mc Donalds
New Zealand: New Zealand Coin & Banknote Catalogue

I have books on Sassanian coinage (Whitting)and Parthian coinage (Sellwood), but I regret not having any decent books on Indian, Islamic, South East Asian or German coinage before AD1600, which Krause does not cover.

Not to forget that there is a huge amount of online reference sources, from which you can draw.

It really depends on which area you're focusing on especially in the US classic coin series. Some series/areas have several books others have one or two.

Westcoin and I have been compiling a listing, not complete by any means but fairly comprehensive, send me a PM if you'd like a copy. I try to add new books as I come across them.

-MV

The RedBook is probably the best book that covers almost all facts one needs to know on any US series, except pricing can be off, the mintage, composition, history, etc. is so easy to use and has been refined each year for almost 60 years now. So for any new collector (or old) that is the best book to start with.

There are so many great books out there on so many different aspects of coin collecting, let us know where your interests lie, and I'm sure I can, along with others here make some great suggestions of books to search out.