For productivity and such, I love Cozi (free) for to-do lists, calendar (app't keeping) and shopping lists, as well as iXpenseIt ($4.99 but WELL worth it) to keep track of our expenses. Evernote, Shazam (if you don't know what or who sings a song, just let it listen to it and it'll tell you) & Night Sky (to see where the planets/constellations are in relativity to where you are positioned) are nice too.
