FlightAware - Track your flight by entering your airline and flight number and receive updates on flight delays, gate changes, and/or cancellations.
XE Currency - Quotes live currency rates.
Perfect World Clock - Provides easy access to the time in hundreds of cities adding several clocks as home screen widgets.
EHU - Helps campers and caravanners keep track of the electrical output of their assorted travel gadgets to avoid overloading the circuit.
Packing Pro - Enter destination, length of trip and who with and it will provide a list of what you may need.
Google Maps - Accurate GPS enabled maps along with voice navigation.
Air Sharing - Turns your iPhone into a wireless hard drive, allowing the user to quickly load documents at the airport that can be viewed in flight.
MoneyPass - Access locations of over 20,000 surcharge free ATMs either by entering an address, a zip code, or using your current location. 
JetLag Genie - Gradually alter your sleep habits before a trip to better deal with jet lag.
Passbook - Passbook is an application in Apple’s iOS that allows users to store coupons, boarding passes, event tickets, store cards, generic cards, and other forms of mobile payment.
Pin Drop - Allows users to drop GPS pins onto a map while traveling of interesting spots or review user made lists recommending the best sights, sounds, and flavors in town.
Urbanspoon - Shake your phone and the Urbanspoon slot machine will suggest local popular east via the GPS in your phone throughout the US, Canada, UK, and Australia.
TripAdvisor - Honest reviews of hotels, restaurants, attractions, and more.
Tripit - Combine all your travel reservations in a single locations.
HearPlanet - The world’s largest audio guide pulls information from Wikipedia and its own database. Similar to audio guides handed out at museums.