The Collins Bird Guide (Svensson et al) is generally reckoned to be the best field guide in the world. If you prefer a photo guide, the Britain's Birds (Hume et al, Wild Guides) is the best.
There are many excellent books on birds and history, poetry, music etc - let me know your tastes and I'll make some recommendations. If you are more scientifically minded there are lots of individual species monographs, from the heavyweight Poyser series downwards.
Birds Britannica by Mark Cocker is a particular favourite, covering bits of folklore etc. For brilliant writing, try The Peregrine by JA Baker.
There are all sorts of site guides telling you the best places to go birding, including a brilliant one on the Scottish Highlands, though modesty prevents me from telling you the author's name <big grin>.
There are plenty of avifaunas, detailing the distribution of birds in a given area.
I've been reviewing bird books for over 30 years and believe me, there is probably a book on every birding topic imaginable - there are thousands of available titles. If you are interested in anything in particular, be it individual species, families of birds, places to go, birds relating to something else and so on, let me know any particular areas you want to read up about and I can make further recommendations.
Hope that helps,
Gordon