Quiet: The Power of Introverts really opened my eyes to the fact that other people feel the way I do and that it's alright to be "introverted". I highly recommend it if you haven't read it and this type of subject matter is enjoyable for you.
I came here to recommend the same book, so I'll just second your recommendation. The writing is sometimes a little too cute for its own good, but it's an excellent read.
(non-affil link) http://www.amazon.com/Quiet-Power-Introverts-World-Talking/d...