You call that a diary?: Many people keep diaries/journals to record their thoughts and note significant events in their lives as well as in the world around them. The memoir is an edited diary where the "author" will compile those entries which are usually the most flattering and/or interesting, and then fill in the gaps and add context to the events. A memoir may be more artistically interesting, and certainly it allows the writer to explain the whys and whatfors, but in terms of history, nothing beats the diary in its pure form.
Comes now Samuel Pepys and his diary from the 17th century. Pepys was basically (and I'm grossly generalizing for effect) a bureaucrat; he was a secretary to a government official for much of his career. However, he also had far-ranging interests from music to government affairs to women. His diary marks some of the most interesting events in English history at that time; from changes in the Cromwell government to the re-emergence of the plague. The website linked above gives us a unique perspective on his diary. Beginning in January of this year, it has published the correspondending day (January 1, 1660 equals January 1, 2003). Most important is that Pepys is unflinching in his writing. He talks of his illnesses as well as his dalliances with women. The man could also drink. But, he is not without insight to the thoughts and ideas of the time. You could do worse than follow along each day with Samuel.