Reading - When Once Just Isn't Enough

There was an interesting article in The Observer last weekend, where a number of writers talked about books they had taken the trouble to read not once, but twice.  The piece was worth reading if only for a perfect image from one of my favourite authors, Geoff Dyer,

I'm not a great rereader – or at least, I'm a failed one: I decide to reread something I read 20 years ago and then give up because the original experience, presumed forgotten, turns out to have been mysteriously preserved, like a leaf between the pages.

 Mostly, I'm an accidental re-reader.  I was completely immersed The End of the Affair by Graham Greene and it wasn't until the very last page that I realised I'd read it before -- I even found the other copy on my bookshelves, testament, perhaps, to having my heart broken too many times. I don't even like Graham Green, that much.

I can think of two good reasons to re-read something: sometimes, it can be like a reunion with an old friend.  I can't bear contemplate ending my days without having read Wuthering Heights again and I've sobbed my way through it two or three times already.  Other than indulgence, it can be useful, as a writer, to re-read something you have really enjoyed the moment you finish it.  Devour it once for pleasure, then go through it forensically for a second time, trying to work out how the magic tricks are done.

With so many fantastic books waiting to be read for the first time, it can seem almost sacrilegious to return to an old favourite.  What books would you go back to, and why?