Midori
I have already commented once about my love of this app (in September). It has now been updated with neat additions (like the animated kanji - yay!) and a vocabulary list by JLPT-levels (double yay!)... It is, in my books, the best kanji app out there... the only other thing I would like (and I hope it gets added in another update) is a FORWARD button so one can move from one kanji to the next when using the lists (so one does not have to go back to the main window to get to the next kanji).
Mirichan about
Midori (Japanese Dictionary), v1.6.1