For information on the chronology of the Roman Emperors, I would recommend Chronicle of the Roman Emperors:The Reign-by-reign Record of the Rulers of Imperial Rome by Chris Scarre. Click here for the amazon.co.uk listing of it.

The book deals with all the Roman emperors from Augustus to Romulus Augustulus, and gives enough detail on each one to give you a basic knowledge about each of their lives without flooding you with information.

There is also Chronicle of the Roman Republic: The Rulers of Ancient Rome from Romulus to Augustus by Philip Matyszak, which talks about the most important people in the Roman Republic (and also deals with the early kings). See here for more.