flippin love Lisbon. Been 5 or 6 times, and i really would quite like to go back this autumn.
Not sure what food etc you're into but a couple off the top of my head (stick em in google maps);
A Cevicheria on Dom Pedro V, cracking cerviche if that's your thing
Evening beer and views in Jardim Sao Pedro just down the way from the above
Vai la Vai restaurant at the bottom end of Bairro Alto
Park Bar (you need to access the ground floor of a multi-storey and choose the top floor in the lift - excellent views. slightly wanky clientele).
Take the ferry over to Almada the other side of the river and walk the old industrial river front down towards the jesus statue
The new resistance museum about the revolution is good if you like history
A number of hotels have rooftop pools/bars with amazing views, just walk in go straight up, the staff dont usually bat an eyelid
Day trip to Cascais, west of Lisbon (beautiful), or Caxias which is closer (students go here)
i want to go back :D
forgot one, there's a good african food place near the castle, i think it's the Cantine, it's got great curry