I read lots of books on the D90. Four actually, including the owner’s manual. Out of respect for the other authors, I will not name those that I liked less. OK, I will mention D90 for Dummies which does get a “runner up award” as being also a good book.
This one is the best. It quickly skips through the basics, which you should know if you are buying this kind of DSLR. After, you probably owned a “point and shoot” before and wanted more control more power and you upgraded to the big leagues.
This book has the most little post-its tags that you have ever seen 🙂 Lots of great tips and tricks.