The two most crowded clubs are Lux (which is a little more "sophisticated" and claims to be mixed, even though it is almost all gay) near Santa Apalonia (you will need a taxi, as they are still trying to figure out how to build a metro station at Sta Apalonia that won't flood), and Frágil in Bairro Alto. Frágil has been around much longer and looks a little tired, but it is always packed.

The bad thing about Lisbon's gay scene in my opinion is that the bouncers charge radically different prices for different people, so dress well (especially at Lux) and if you have a Portuguese friend, enter with him.

For restaurants, I like Senal Vermelho for Portuguese food in Bairro Alto. It has a lot of tourists (usually earlier) but it is very popular among Portuguese too. Casa Nostra is good for Italian.

Make sure to see the (straight) bar Pavilhão Chinês. It's fascinating - the owner collected millions of little things to put into the bar. One room, for example, has thousands of toy soldiers.