I am halfway through an excellent book I received in the mail yesterday: Seneca: The Humanist at the Court of Nero, by Danish thinker Villy Sørensen.  I’m finding it an enjoyable and compelling read, without being technical.  Sørensen published this biography in 1976, and it was translated into English by W. Glyn Jones in 1984.  Sadly, it is currently out-of-print, but used copies can be found for a reasonable price (I ordered a very good copy via Amazon for $10 USD). 

If you are interested in Roman history and politics, Stoic philosophy or ancient philosophy in general, I highly recommend this book.