Scottie's apartment (900 Lombard Street) is one block downhill from the "crookedest street in the world". Although the door has been repainted, the entrance is easily recognizable save for a few small changes to the patio. The doorbell and the mailbox, which Madeleine uses to deliver a note to Scottie, are exactly the same as they were in the film.
Here is a link to the wikipedia film entry which includes information on Vertigo filming locations:Read film information at Wikipedia
For more information about this and other Classic Movie Travels, see the book Film + Travel North America, South America: Traveling the World Through Your Favorite Movies