The best Ive found.

I am learning Japanese because my fiancés family is from Japan and we have a baby on the way, who we want to raise in a bilingual environment. This program covers all of the hiragana, katakana and a good chunk of kanji. There are limitations to what an iPhone app can teach about a second language but this is a great way to cover the basics.

Opiate1984 about Learn Japanese with Phrases & Lessons, v3.3.7