You can read it here
http://www.archives.gov/press/exhibits/dream-speech.pdf
Incidentally, please do take the 17 minutes to watch this speech (and perhaps follow along with yread's transcript link). It really is one of the greatest speeches ever given.
In the case of the text, it is possible to find copies online (for, via the National Archives), but redistribution in other printed works (namely, textbooks) is problematic.
As for the video, the King estate controls that very, very tightly.