I have iAnki, which is more of a web app, but still really useful when i want to do my daily review and adding away from home/computer.
Human Japanese light
A great app with really detailed info for beginner japanese, i probably wont buy the full app cause i think ive already studied whats in it, but i would recommend it to any beginners learning japanese, its really good to start learning japanese. I wish i had it when i was beginning japanese.
Word power lite
Made by Innovative language learning, who are the guys who do Japanesepod101. It gives you a different word every day and lets you put it into a word bank. its very mediocre.
Kotoba
A pretty normal j/e e/j dictionary based on the wwwjdic files. its free, but im still waiting for a legit, J/E E/J High quality Legit Dictionary. Theres the WISDOM dictionary on itunes but it doesnt have furigana, which is pretty much a must for me right now, cause i dont know enough kanji. Biding my time....