What i liked most about Pliny's letters were the insight they gave to the world around him, granted it was limited from his own point of view and social class, but nonetheless to hear a voice from the past in such a way, with his daily preoccupations and concern for friends was very interesting.
What historical sources are fascinating in a similar manner? What voices can we hear as clearly as Pliny's? I have no preference as to what place or time period the source may be from, only that it concern real people and their own personal thoughts and opinions.
If you liked the letters of Pliny perhaps you'd enjoy The Letters of Fronto. Fronto was the tutor of Marcus Aurelius and Lucius Verus. The letters are Fronto's correspondence with various emperors and others. They range from mundane things like health and small talk to official letters in regards to duties.