A book I’ve been mentioning (and will continue to use in my entries) is:
If you like research on bipolar disorder and/or recurrent depression, this is the freaking awesomest book ever – a huge collection and summary of available research on every aspect, with commentary. If you like it enough to consider getting it, I encourage you to get it through the link above, which will benefit crazyboards, the support and education boards that I help moderate and that have helped me a whole hell of a lot.
If you can’t afford the price tag, you may be able to get it through inter-library loan. The current one is the second edition.