About Hostel Discount Cards:
International hostel organization YHA (Youth Hostel Association -- or HI-- Hostelling International) issues hostel discounts in exchange for membership, and some independent country-based hostel organizations offer discount cards. Most student discount cards don't offer a hostel discount -- read on for a list of hostel discount card providers.
YHA, or HI Hostels:
Youth Hostelling Association (YHA) or HI (Hostelling international) has a hostel membership and governing body (International Youth Hostel Federation) and hostels belonging have to conform to some standards. Sort of like a hotel chain, you can expect a clean, decent hostel if it belongs to HI, but don't expect any central service from HI. About.com's Student Travel Best Hostel 2005 is an HI hostel. Annual $28 HI membership gets you a discount at HI hostels plus deals and bennies.
Nomads World - Hostels Plus:
Australian travel agency Nomads issues a young-at-heart travel card good for $1 off a hostel bunk in Australia, New Zealand, Fiji and London, as well as calling cards and discounts on Oz Greyhound buses and Great Southern Railway trains. Get the card online or at a Nomads member hostel.
Hostelworld Gold Card:
Hostelworld's gold card gives a $2 discount for online hostel booking only -- no additional discount at the hostel itself. You get one free with an ISE membership, and an ISIC card waives the $2 Hostelworld.com booking fee. The card alone is cheaper (about $15) than either of those student-youth travel cards ($20+), which offer additional discounts. Will you book at least eight hostels online but need no other discounts? Then it might be worth it.