Shazam has already been mentioned. That, and Google Translate are 2 apps that make me feel like I am living in the future.
Hear a good song in a restaurant? Now I can find out who it is.
Want to understand the instructions that are written in Italian? Take a picture and let google translate.
Chatting up a cute french girl who doesn't speak any English? Say "You have very pretty eyes" to my phone and listen to it say "vous avez de tres jolis yeux"
Of course, I have never been in a situation where I needed these capabilities but they do amaze me.