We stayed at Welcome Guest House for three nights and really enjoyed it. It is very central (walking distance from almost everything in Lisbon), cheap and very clean. There is a beautiful staircase to walk up to the rooms and a communal kitchen that is small, cosy and clean. You can eat on the nice small terrace. The staff is very friendly and accommodating, although sometimes hard to get a hold of. The beds are very comfortable (although very squeaky). Great place if you are looking for cheap and simple accommodation.