Aside from exploring the city streets at your own leisure, some sites worth seeing (in addition to the pyramids and the sphinx) is the mosque of Muhammad Ali, the Egyptian Musuem, Tahrir Square, Old Cairo, and the Khan El-khalili bazaar. A simple google search with show you many more mosques, museums, and bazaars to see but this list is a good representation of all of them, especially good if you are short on time in Cairo.