History of the original Caligula
I fully intend to write my own paper on Caligula in the future, but for now I will just provide some links to sites that together give a well-rounded view of the man.
PBS.org Special - The Roman Empire in the First Century - Years of Trial - Caligula
Joan's Royalty In History - Mad Monarch Series - Gaius Caligula of Rome (my favorite)
Online Encyclopedia of Roman Emperors - Gaius (Caligula)
Roman-Empire.net - 'Caligula' Gaius Caesar Augustus Germanicus