Bright Lights, Dark Shadows
This is a massive book at 568 pages. It covers the history all the members of ABBA, Stig, and some others related to their work. It includes a number of photos, a list of sources, and one tremendous amount of information on the group.
What is one of the best things about the book is that it is readable. You end up glad it's so long since you can learn so much about ABBA and not be bored out of you skull by badly written, uninteresting material.
If you collect ABBA things you absolutely must add this book to your collection and read it, both!
Main ABBA Index