This fast dictionary can be used as the default look up dictionary on those Kindle devices that allow it*. (NEW: the Kindle app for iPhone, iPad etc. now can use this as the default dictionary!)
The main features are:

More than 170,000 entries! (Based on JMDICT: EDICT's big brother)
Fast look-ups while reading
Phonetic reading is prominently displayed
Easy to read layout
Thousands of example sentences
Words within the dictionary (e.g. in the examples) can be looked up as well!
the entire dictionary is cross-referenced!
All words indexed both in Kanji and hiragana
syntactical, usage, source, etc. information is presented in easily readable form.
Now with a quick grammar reference!

Just set the default Japanese dictionary on your Kindle to this dictionary and start reading!

*Note: Kindles with keyboards can not efficiently do dictionary searches in Japanese. Those Kindles rely on spaces to determine word endings, and as Japanese doesn't use spaces, the Kindle will only look up the first character after the cursor. Therefore, there are no good options for those models, unfortunately.