Hostelling International
For booking hostels you may use this site and for booking a hotel you may use hpb.
Hostelling International (in the past - International Youth Hostel Federation (IYHF)), is the federation of more than 90 national youth hostel associations (such as Youth Hostels Association, American Youth Hostels, YHA Australia and many other) in more than 80 countries who run over 4,500 youth hostels and youth hotels around the world. International hostel organization (Youth Hostel Association or "HI" - Hostelling International) issues hostel discounts in exchange for membership, and some independent country-based hostel organizations offer discount cards. Be aware that most student discount cards do not offer a hostel discount, you have to check beforehand whether your discount card is equipped for this.