Hostels remain the cheapest way to score accommodation when you're seeing the world (assuming security issues don't drive you to a hotel). iPhone application Hostel Hero lets you search for and book hostels in 150 countries, and stores details of your bookings on the device itself.
Check out the video for a full roundup of features. Lifehacker AU doesn't run to a test iPhone, so I'm not sure how well the app works in practice. Hostel Hero is free to download, but charges one UK pound for each successful booking. If you give it a spin, let us know how it goes in the comments.