Very relaxed chain of hostels with two locations in Amsterdam. The guys who run these places are travelers themselves, which is why they cater so well to backpackers. Both of these hostels have private rooms, too.

The Flying Pig Uptown - Vossiusstraat 46 (near Vondelpark)
The Flying Pig Downtown - Nieuwendijk 100 (near Central Train Station)

Visit www.trippist.com for more local & budget info on Amsterdam.