The first Beatles tell-all that I read was The Love You Make, by Peter Brown, when I was 13. This lurid bio had me mezmerized (the book opens with Cynthia catching a drug-addled John with Yoko in 1968 ), but the consensus amongst fans and the band themselves was that this was gossipy, scandal-ridden and trashy. While I don't disagree with that, let's face it, the Beatles did a ton of drugging and whoring during their day, so who's to say it should have been suppressed?
The big coffee-table book The Beatles Anthology (a companion piece to the DVD series) is probably the best book: it's got a massive number of great photos, and the entire story is told by the Beatles and the inner circle. It could be said that because the Beatles told their own story, it's a sanitized version; but I don't get that impression from reading it. They all tend to be pretty honest. The main drawback is the size of the book -- you can't exactly whip it out and read it on the bus.
The recent book The Beatles (the author's name is Spitz, I believe) looks pretty great, too, from the excerpts I've read.