Marques de Pombal
Top of Parque Eduardo VII
Many different
viewpoints (miradouros) of Lisbon (some of the ones above are on the list)
Oriente in Lisbon (especially the Vasco da Gama bridge) for the "new" Lisboa
Many scenic places in Sintra
This won't be very helpful, but somewhere in Alfama, at the very top of a hill, was a large square overlooking the city below, which was really spectacular. We found it while wandering, so maybe someone else will know what it's called.
map (also on the list above)