Today might have been known as Halloween for most people, but for Christians this is the day that we remember and acknowledge a great moment in Christian - and world - history.
"I would never have thought that such a storm would rise from Rome over one simple scrap of paper..." (Martin Luther)
It was on this day, 1517, that Martin Luther nailed his 95 theses to the door of the Wittenberg Cathedral, thus igniting the Reformation in Europe and calling into question the accepted and previously undisputed practices of the Roman Catholic Church.
"Hier stehe ich. Ich kann nicht anders. Gott helfe mir. Amen." ("Here I stand. I can do no other. God help me. Amen.")
Many resources are available all over the web, but here are the best I found:
Martin Luther: Lessons from His Life and Labor, a biographical sermon delivered at a conference by John Piper. Read or listen to it here.
A PBS page on the famous monk. You can learn about his life and teachings in a nutshell, as well as watch a few interviews, two of which feature Alister McGrath.
The nearly inexhaustible Wikipedia page. With a complete timeline of his life and teachings, as well as external links, you could spend a lot of time there.
And then, you can always pick up one of his books, or sing the hymn he is most famous for:
A Mighty Fortress is Our God.
(Here you can listen to the American Boy Choir's beautiful rendition for free.)