I was watching the episode of Charmed where they go up against the Four Horsemen of the Apocalypse. I thought I'd google it and see what was there.

http://www.apocalipsis.org/fourhorsemen.htm

http://en.wikipedia.org/wiki/Four_Horsemen_of_the_Apocalypse

http://www.gotquestions.org/four-horsemen-apocalypse.html

http://www.revelation13.net/horsemen.html

http://www.gotoquiz.com/four_horsemen_of_the_apocalypse

There are also several very cool images to be found: