When I worked at the School District of Philadelphia, I would get the Martin Luther King holiday off of work. I wasn't the kind of person that would volunteer to build schools, I always had enough of my own projects to do. What I would end up doing was to have the TV on and get caught up in my home.
One year I got the bright idea to leave the local PBS TV station on when they ran a day of programming about the Civil Rights Struggle. I'm a documentary junkie so I got my fill that day. They did run the I Have A Dream Speech as well as many others, and what I was left with was more than just a sense of history, but a deep sense of loss that this man, Dr. Martin Luther King didn't have more years to share his vision.
The few speeches that did get recorded were always worth listening to, and always fascinating both in and out of context.
I managed to find a place to pull them down on MP3 and loaded them on my trusty player at one point. Listening to them on the way to and from work on the train happened more than once, they did get into "rotation".
No matter what your political bend, the time spent listening to this man is well worth it.
Since the I Have A Dream speech is available readily online, you can find it here.
As for the other ones, I'd say happy listening. Many of them are available in random places, and I did find a helpful web site at Stanford University with a list of some of them for your clicking pleasure.