英辞郎 - Eijiro dicionary (ALC)

You can purchase a copy directly from eijiro:

http://www.eijiro.jp/

Also, the Japanese Language Tools site offers a EPWING version for purchase:

http://www.japaneselanguagetools.com/busOther.html

I originally bought the EPWING version from this site several years ago for an old Palm Treo, and last year I transferred it to an Android phone with great success.