Hostel Memberships
There are several hostel networks in Europe which provide discounts to card holding members. YHA and VIP are the major players.

		VIP Hostels VIP is very well established in Australia and the number of member hostels are slowly growing in Europe. A VIP membership costs $25 and you get a useful book with a list and description of all VIP hostels worldwide. VIP membership comes with lots of discounts in Australia, but not so many in Europe. Kirsty's Opinion - There are more VIP hostels in major European destinations than HI Hostels, and they tend to be more interesting, so I would choose this membership card if I was only buying one.
		Hostelling International (also YHA) YHA (Youth Hostel Association) and HI (Hostelling International) are the exact same company that goes under different names to confuse us poor backpackers. A card lasts for a year and costs $$$, but stamps can be accumulated as you stay in YHA/HI hostels to the point where you get a free card after six visits. The discount is generally a set nightly amount and the YHA/HI doesn't usually get you discounts on anything but hostels. Kirsty's Opinion - Most smaller cities in Europe with only one hostel are affiliated with YHA/HI so if you plan on getting off the beaten path a little bit, then a YHA/HI card will probably pay off since you won't have much choice but to stay in their hostels. I find their member hostels to be sterile and dull for th emost part, so they're not generally a place to come if you're looking for a party. On the other hand, if you're travelling with kids or your parents or something, then YHA/HI would be a safe bet as they're always clean and secure.
		Hostels of Europe 'Hostels of Europe' was once a card for discounts at a small group of independent member hostels across Europe. I'm not sure what happened, but the card no longer exists. The website has instead become an affiliate of Hostelworld.com and provides online bookings through them, rather than using their old, independently run system. Their website still offers what seems to be a 'Hostels of Europe' membership, but it's actually a yearly membership to the Hostelworld.com site which eliminates the $2 online booking fee but doesn't actually give any discount on the prices of hostels. Kirsty's Opinion - This isn't actually a membership card anymore and will only get you discounts on online bookings made through sites which are affiliated with Hostelworld.com. Don't be conned! If you plan on booking a lot of hostels online then it is worth it to buy the Hostelworld.com membership, but you might as well buy it from them rather than supporting this sneaky site.