Library Recommendations

By "As many coins as possible", I assume you mean "the entire worldwide history of coinage". Here's my list of most-used books in my library:
Ancients:
- David Sear's catalogues, of Greek (2 volumes), Roman (four volumes), Roman Provincial (1 volume). These cover most of the "classical ancient world".
- For fringe cultures, barbarian empires etc., I use Wayne G Sayles' "Ancient Coin Collecting Volume VI - Non-Classical Cultures".
- "Classical Deception" also by Wayne G. Sayles - to clue up on the counterfeits.

Mediaeval: There isn't much to cover this period.
- I have Philip Grierson's "Coinage of Medieval Europe", but it's more of a coffee-table book than a comprehensive guide. Still useful though. The comprehensive multi-volume catalogue, "Medieval European Coinage", is hideously expensive.
- David Sear's book on Byzantine Empire coins.
- The Spink catalogue of English coinage. The Coincraft book was apparently better, but is no longer printed. There are Scottish and Irish volumes, too, but I don't have them yet.

Chinese
- The David Jen catalogue "Chinese Cash" put out by Krause suits my needs. The work known as "Fisher's Ding" is more comprehensive, but less available.

Islamic
- Richard Plant's book "Arabic Coins and how to read them" is an excellent teach-yourself-numismatic-Arabic textbook.
- Stephen Album's "Checklist of Islamic Coins" is the standard reference work. Unfortunately, it's got no pictures!
- Album's reworking of the 1869 catalogue by Marsden, "Numismata Orientalia Illustrata", has the pictures you need to go with the other two books.

Modern
- The multi-volume (five, at present) Krause "phone book" catalogues. Covers 1601 to date.
- The Krause supplementary catalogue, "Unusual World Coins", to cover the "weird stuff". It's not always easy to tell apart the "Liberty Dollars of the world" from the "real coins".
- I've been referring to my Conder Token book a lot recently, too - I think they're becoming more mainstream. All I've got is a tiny, old British booklet by Seaby. If you can do better than that, please do so.

This covers almost all coinage known to man. But there are still some annoying gaps:
- just about everything in between 1450 (when Grierson's mediaeval book finishes) and 1601 (when the Krauses begin). I await with bated breath Krause's expansion backwards in time to cover this period.
- mediaeval non-Chinese, non-Islamic Asia - places like Sassania, Trebizond, India, Southest Asia, Japan, etc.

Edit to add: Also handy: "The Coin Atlas" by Cribb, Carradice et al. Excellent overviews of every country's coinage, from ancient times to today.

Official Price Guide to Mint Errors 7th Ed. by Alan Herbert is a great reference book for descriptions of the various classes of errors and die varieties. He uses the PDS system (planchet, die, strike) for classification with good descriptions and many photos.

A good general reference/info book would be The Expert's Guide to Collecting & Investing in Rare Coins by Q. David Bowers. It gives a general overview for each denomination series and also covers subjects such as paper money, tokens, and colonial currency.