On BBC Radio 4 this morning I heard of a government initiative, "Books on Prescription". It's a list of self-help books drawn up by some committee as actually having evidence of usefulness, and which are to be made available in all public libraries. They give a list of evidence-based references.
General page for Books on Prescription.
The evidence, a list of scientific studies in the literature.
I have not read any of the books (which is why I'm not posting this in the Media Thread), but I notice from the titles that a lot of them are based on Cognitive Behavioural Techniques, which are generally well thought of on LessWrong.
The site also mentions a set of Mood-boosting Books, "uplifting novels, non-fiction and poetry". These are selected from recommendations made by the general public, so I would say, without having read any of them, of lesser expected value. FWIW, here's the list for 2012 (of which, again, I have read none).
I notice that almost all of those books are about things that are considered "mental problems" (the exceptions being chronic fatigue, chronic pain, and relationship problems, which are nevertheless specific problems). So if a self-help book isn't about a particular problem (like How to Win Friends and Influence People and The Seven Habits), or the problem it talks about isn't primarily psychological (like Getting Things Done), then it won't appear on that list regardless of how good it is.
(Stating my opinions here so that you won't have to guess:...
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.