renzo Inc. has Japanese (iTunes Link) for the iPhone, iPod Touch, iPad in the iTunes App Store for FREE (regularly $6.99) for a limited time.

This Japanese/English dictionary is massive, yet easily fits inside your iPhone or iPad. Contains more than 174,650 entries and 52,000 examples, as well as stroke order animations for kanji and kana. Japanese works completely offline, an internet connection is not required. Updates are free.