Dirty Harry scene
The sequence when Toschi and Graysmith are watching Dirty Harry at the cinema takes place at the Northpoint Theater, which was an actual movie theater in San Francisco during the 1970's. The theater closed in 1997, however, David Fincher had his production team re-open / dress it for filming purposes to add realism. I can't think of many film makers that would go to all that trouble for historical accuracy. I noticed the theater while reading J.W. Rinzler's 2007 book The Making of Star Wars. In the book, there is a photo of the theater where Star Wars is playing along side the Paul Newman film Slap Shot. A couple of days later I spotted it in Zodiac.
Great book for Star Wars fans.