Today I bought an ipad! When I got it I immediately went into to app store on a hunt for apps that would help me learn Japanese, this is what I found;

• Hirigana and Katakana - Complete Basics of Japanese    This is a good free app for learning Hiragana and Katakana
• Study Japanese for iPad    This is another good app for learning Hiragana and Katakana, this is however better than the last one in my opinion, for example you can draw the characters in it. This is not free.
• Learning Japanese (It's easy to find by searing for Tae Kim)    This is an amazing free app. It is basically a boo kand it teaches you about Japanese grammar.
• Learn Japanese Vocabulary - Free Gengo WordPower   This is a good one for expanding your vocabulary, there is a also a better paid version of it. 
• Japanese Language Guide    This is free and gives you lots of little phrases that are nice to look at and learn.