I was very excited to see the American Reunion movie. I saw American Pie just after college and remembered it was quite funny.
Jim, Michelle, Oz, Heather, Stifler reunite for their high school...
There's the art gallery of NSW (if you're into that). There's usually something going in Darling Harbour at the weekend. Centrepoint Tower gives you a fantastic view of Sydney. You can always take a ferry over to Manly and visit the beach. There's a place called The Rocks which is mostly full of pubs and bars but it also has historical tours you can take.
The Royal Botanic Gardens are very nice if you feel like wandering around a park for a while(find the bats/flying foxes at dusk! Aussies... is there a difference?). The Sydney Aquarium is pretty great. I'm still kicking myself for taking photos of the fountain from the Matrix("freeze it!") and not realizing it was the same fountain until I got home. Would have had some cooler framed shots of it otherwise(I can't remember if it was in Strand Arcade or not). Walking under the Harbour Bridge is pretty great too due to it's sheer size.
If you have time then visit the blue mountains. Beautiful scenery, just a couple of hours outside the city. You may remember them from MAD MAX BEYOND THUNDERDOME, although they were covered in sand. (When they arrive at the kids hideout)