I highly recommed Elisa's flat. It's even nicer than it looks on the pictures. It has everything that one needs. I stayed there for ten days with four friends. Sometimes we cooked at home - the kitchen is very well equipped, there's a dish washer and also a washing machine. It's in a quiet neighborhood, but at the same time there are many nice cafes in the vicinity. Trastevere is a scenic and not so touristic part of Rome. It's easy to walk to the Center or use public transport.