By far the best books to read when one is blue, or bored, or desperate, are the books one is most familiar with. I often go back to those I loved as a pre-teen; the ones I read over and over and formed so much of who I am today. One of these is The Long Secret
Also good when I'm in that kind of mood are books that are so predictable one can figure out from the first page what the denouement will be, and one forgets the whole story within minutes of completing the book. Often, these are books penned by authors who can only write one kind of story, so all their books are pretty much the same -- but so comforting, like hot soup. One whose adult novels are now out of print, but is experiencing a renaissance as a childrens' writer is Eva Ibbotson. Her adult novels used to be shelved with the bodice-rippers at the library I patronized as a teenager, but her books couldn't be more different. They're all at some point before 1940, and tend to wander around Europe a bit. There's always a nice female protagonist who's rather special in some way (this varies); a man or two is involved, and one is really nice. Even the one who isn't nice isn't especially nasty. My personal favorite is Madensky Square, but the others are just as good (and just the same, I might add).
I can't sign off without mentioning Rosamund Pilcher. Her books are so comfortingly written, and her characters so likeable, that the reader finds herself (sorry, really not "guy" books) condoning the most immoral behavior on their parts. I must have read The Shell Seekers
So now it's your turn -- what are your guilty pleasures?