Accommodation
Hostels
Rede Nacional de Turismo Juvenil runs the Lisbon hostel, which is near Picoas Metro) at the north of the city centre. This is cheap, but prone to being fully booked, and has all the downsides of HI hostels everywhere. They also run the Parque das Nacoes hostel, which is located out of town at the site of the 1998 Expo. This is quite close to Oriente station, so could be convenient for late arrivals or early departures.
Lisbon is one of only a couple of cities in Portugal to have decent independently-run hostels. Currently there are two. The Lisbon Lounge Hostel, which is close to Cais do Sodre Metro, is an extremely welcoming small hostel with free internet. The Poets Hostel which is near to Rossio Metro. See the websites for these hostels for details.