History of Dota (There are multiple episodes which are linked on the video)
Dota 2 Links:
Unfamiliar with Dota 2?
http://www.freetoplaythemovie.com/ Watch the Dota 2 Movie!
A Youtube Playlist for Dota for Dummies
A Steam Guide for Dota
Reddit Hero Discussions
Learn Dota in 4 Minutes
Switching From LoL? Here are a few different Reddit threads about People asking Questions and Explaining Major Differnces and General Advice