Isolde, great taste in reading materal! I love Mists of Avalon, one of my favourite books, and also the hitchikers guide series is extremely good. Two more books I think should be mentioned are
Give a Boy A Gun I think it's by Todd Strasser. It's about these two school shooters, but it's told from their friends, family and classmates, through excerpts. it's really good.
AND
The Count of Monte Cristo by Alexandre Dumas. A classic tale of revenge, and how it can suck you in, until it's all you think about.
Oh, yes, almost forgot
The Outsiders and pretty much anything else by SE hinton. Very insightful. I find the young adult books to be more insightful than the horrible attempts at fiction I've seen recently. Then again, i read a bit too much for my own good (I spend 4 hours weekly in the local bookstore, at any point in time, i have at least one canvas bag full of books that I took out from the library) and am highly critical. But those are the most insightful books I've read that haven't been mentioned yet.