Theres a new one out, one of those "For dummies" books, I bought it to help my family undersatnd the illness, its called Bipolar for dummies, and is by Candidia Fink, it really is what the title says and helps friends and family understand me.

I think these have already been mentioned but Electroboy & An Unquiet mind are great, however when reading some parts of Electroboy, I kinda missed some things!

Another useful one is
"Coping with bipolar disorder" by Jones Hayward & Lam

Best of luck!