Travel Technology - iPhone/iPod touch owners, What's your favourite application?

Hi guys, I just got my iPod touch, I'm just wondering what's your favourite application/games?

I use Yahoo Messenger to chat with my family no matter where I am.

Instead of starting a new thread, a quick search would have turned up this extensive discussion:
http://www.flyertalk.com/forum/travel-technology/848219-favorite-iphone-applications.html