A good short general introduction is from the National Park Service (because the route is now a National Historic Trail). Click here and here. You can also find a longer, more developed essay here from Stanford University's King Encyclopedia.
There are a wide range of excellent video resources. Here is a sampling. This short video (6:37) is an excerpt from the PBS "Eyes on the Prize" video series:
Finally, this video (10:44) from the LBJ Library shows President Lyndon Johnson discussing his meeting with Alabama Governor George Wallace one week after Bloody Sunday