Favorites:
Interference
Siri -- speak or type whatever you want (movie times, directions, "what's happening at madison square garden tonight?") and it gives you the info, directions, phone numbers, ticket ordering, etc.
RedLaser --- already recommended by Sicy & awesome.
Bump -- swap info, pics, and now music (?) with another iphone
SoundHound -- better than Shazam because you get unlimited free song recognition
Grocery IQ -- make grocery lists, organize them, and best yet--multiple people/phones can edit the same list (so Mrs. Utoo and I can edit the same list whenever we think of something)
Genius Scan -- Take a picture, crop it, and turn it into a PDF--good for taking pics of paper documents and making them computer files
Google Translate -- type or speak in almost any language and get the translation written or spoken back to you
HeyTell -- essentially turn your phone into a walkie-talkie