BeWelcome - Open your door to the world!
Trustroots - Travellers community for sharing, hosting and getting people together.
Worldpackers - Exchange your skills for accommodation
Couchsurfing - CouchSurfing is your ticket to explore the world -- from the road or from your own home.
Hospitality Club - Free network of people around the world who offer free accommodation, advice and help when they are traveling - hospitality exchange. Free membership.
FairBnB - A smart and fair solution for community powered tourism.