Waze for traffic and navigation. Nice combination of social and mapping. I just turn it on without routing on my work commute. I get fairly accurate road hazard and speed trap info and people actually thank me for reports that I post.
Audible for ebooks. Subscription service but it means you can get recent publications of decent books (one a month for the subscription) or more if you are willing to buy additional credits.
Airbnb for finding some cool places to stay while traveling
Flighthero for tracking airplanes that are enroute. I recently flew back to DFW from LA. A friend of mine gifted me with a few hours of inflight WiFi so I used it to track the plane I was in just for shits and giggles.
WeatherTap for... weather
iCitizen for political information
BillGuard syncs with your bank account and gives you decent warnings about unauthorized transactions
HBOGO and Showtime has one too. If you have HBO as one of your premium channels, you can stream anything HBO to your device
ZocDoc handy for finding a doctor or specialist near you
IMDB because I can never remember the name of that actor, you know, the one that was in Space Truckers and had a great scene in True Romance with that other actor, you know, the one that was so ugly. He was in Prophecy with what's her name.
Or, just take the time to go looking for an app every time you come across a situation or issue that could be aided by access to your augmented cloud memory.