River Song's diary

River Song kept a diary over her adventures with the Doctor. The book itself was blue and resembled the outside of the Doctor's TARDIS. Since the diary was written from River's point of view, she didn't let the Doctor read it. (DW: Silence in the Library/Forest of the Dead)

History
During the events of the crash of the Byzantium, Amy asked River what her diary was, to which the Doctor told her to stay away and that it was his future. (DW: The Time of Angels)

In the 52nd century, in the Stormcage Containment Facility, River wrote in her diary before receiving a phone call from Winston Churchill and escaping. (DW: The Pandorica Opens)

After the Doctor reset the universe, River gave Amy her diary as a wedding present, though all the pages were empty. This helped Amy to remember the Doctor and bring him back. Later, the Doctor returned the diary to River, telling her that the writing had all returned, but that he had not peeked at it. (DW: The Big Bang)