I can't seem to get this posted on the iPhone apps section. But I just wanted to past along the message on some useful and nifty apps that I use in my travels. I hope others can add to the list;
XE Currency (Free) - Currency converter
MetrO (Free) - finds the best public transportation route from your current location to your tourist destination (ie. Sheraton Hotel to Prado Museum). Currently supports over 400 cities.
Air Canada (Free) - love it or hate it, but since I travel 99% on Air Canada and it's partners, it's convenient for web check-in (on select int'l cities) and viewing your Air Canada flight information.
Flight Update ($4.99) - Keep track and receive updates on all your flights. Get up to date information of your gate number, baggage claims, delays/cancellations, departure/arrival times/terminal, aircraft info before even stepping foot in the airport or when waiting to deplane for your connection. Supports numerous airlines, such as the major and budget carriers (EasyJet, RyanAir etc).
DocsToGo ($4.99) - view/edit MS Office files, view pdf files. I have all my travel info/itinerary/schedules in excel, word or pdf files.
Postman ($0.99) - email digital postcards using templates and your pictures.
Fring (Free) - keep in touch with family or friends on all your favourite social networks including Skype, MSN Messenger, Google Talk, Twitter, Yahoo! and AIM. You can do VOIP over wifi.
White Noise Lite (Free) - Ambient sounds to help you relax or sleep. Quite handy when you need to get some much needed rest while in transit plane/train/bus. There is a paid version ($1.99) which offers more sounds.
WeatherEye (Free) - Get short (1day) or long (7day) weather forecasts of cities. It shows current day's weather in detail. You can set up your home city (ie. Winnipeg) as well as other cities (my favs Madrid, Tokyo, Vancouver). I think this app is better than Apple's built-in weather app.