Hostelworld/Hostelbookers (click here):
With over 36,000 properties in 178 countries with over 13 million verified guest reviews and 24/7 Customer services, Hostelworld is the authority on booking hostels.

CouchSurfing (click here) is a website where you can connect with people all around the world who offer you a place to stay for FREE. Besides accommodation and connecting with people in those locations it is a great way to meet people who can sometimes tell you about their country/culture, show you around, answer questions, practice languages, etc. It also a social networking service that has a mobile app and you can find groups, activities, etc…

Airbnb is an online marketplace that connects people who want to rent out their properties s with people who are looking for accommodations in that locale. It can be a bedroom in an apartment or the whole apartment and is usually cheaper than a hotel, but giving you the comfort and convenience (like a kitchen) of a private property. It currently covers more than 81,000 cities and 191 countries worldwide.

Volunteer/Work Abroad
If you are interested in volunteering or working abroad in exchange for accommodation and food see click here