To see Lisbon, you need to spend several days here. The most impressive building in all of Portugal to my mind is St Jeronimos's Monastery located in Belem (an area of Lisbon). Other places to visit are Belem Tower, Estrela basilica, St. Jorge's Castle, the Ajuda Palace, National Coach Museum, National Tile Museum, Calouste Gulbenkian Museum, the church and monastery of Sao Vicente de Fora, and the church of Sao Roque.
Outside of Lisbon (in suburbs) visit Queluz Palace, Sintra Palace, Pena Palace, and Mafra Palace. Each is very different and interesting in its own right.
Quick Tips:
Queluz, Sintra, and Mafra palaces are free on Sunday 10am–1pm. Except for palaces and St. Jorge's Castle (Castelo de Sao Jorge), most other places are closed on Mondays -- check before you go. The best place to check is the magazine
Lisboa Step By Step" and the website of the Portuguese Tourist Office. Request brochures from the tourist office to plan your lodging and sightseeing. This is the most complete resource I've found on each province of Portugal. The brochures list hotel e-mails and websites.
Best Way To Get Around:
If you are good at driving stick shift, driving in Lisbon shouldn’t be much of a challenge, except that in a lot of places, you may need to go for several blocks to turn in the direction you need since a lot of streets are in one direction. I, however, wouldn’t recommend driving in the city center where the streets are narrow and uphill, and you are competing with a tram and a bus on the same narrow street. Parking is a serious problem, the city has grown so much and there are so many cars, but parking places are very scarse.
Metro costs 65 cents per ticket or 10-ticket card for 6 euros. If you will be using buses, trams and metro, you can buy a daily pass for 2.85 euros or five-day pass for 11.35 euros. Metro is easy to navigate, just follow the arrows and check the metro map and you won't get lost.