Anthology.
If you've already read that one, I'd suggest Many Years from Now (Barry Miles) and Can't Buy Me Love (Jonathan Gould).
If you love recording stores as much as I do, I highly recommend Recording the Beatles and the Complete Beatles Recording Sessions (in spite of the latter's occasional mistakes...Lewisohn isn't quite the "expert" he's known as, and needs to sharpen up his grammar. But it's still a fascinating book).
Books to avoid: Shout (grumpy and dreary), the Illustrated Record (disgraceful errors abound), and Revolution in the Head (critical of many Beatles songs...the author hardly even seems to like the group. The book's popularity still confounds me). If you like "analysis" of any sort, Tell Me Why by Tim Riley is much better.
An interesting glance at how the Beatles were perceived by ex-hippies in 1977 is provided in the Beatles Forever (Nicholas Schaffer), while the Long and Winding Road by Neville Stannard is still the most interesting discography (in terms of reading entertainment), even if it's not the most complete. What I'm really looking forward to is the upcoming Beatles book by Kevin Courrier, the best Zappa author to date.