Left: St. Edward's crown, worn by British monarchs
True, I am a history geek, and I am working toward my PhD in European Expansion.
But how cool is a website that lists every known ruler and head of state, plus other figures like popes, patriarchs, and archbishops?
Way cool, in my opinion. Check out Rulers.org for all of those useless bits of trivia that win bar bets and keep doctoral students on their toes.
The site also provides month-by-month summaries of important world events.
A hat tip to Miland at World History Blog for this reference source. He adds that he has found a few missing pieces of information, such as the monarchs of the 19th-century Hawaiian Kingdom, but I was unable to find any factual errors in my hour of perusal.