They are still writing BlackBerry books right now and none are as good as RIM's website, so the best book right now to get is a book on "J2ME" development. Try searching for "J2ME" or "Wireless Java" at
http://www.amazon.com ... Some have chapters specific to BlackBerry.
Recommended Amazon Search Keywords- J2ME
- MIDP
- Wireless Java
- Java 2 Micro Edition
- BlackBerry Development
Partial Amazon search results found (can't vouch for these recommendations, use your own judgement.)
Core J2ME Technology (4.5 stars out of 5)
O'Reily Learning Wireless Java (4 stars out of 5)
O'Reily J2ME In A Nutshell (3.5 stars out of 5)
Java 2 Micro Edition: Professional Developer's Guide (3.5 stars out of 5)
(And there are at least 100 other search results, some may be better)