Outline of changes to the iOS Developer Program License Agreement
There is a very nice site that publicly calls out changes to Apple's developer terms.


http://www.appstorereviewguidelineshistory.com


Before them, I've not seen anyone that provides these publicly, so I've resorted to saving the PDF to a folder every time I'm prompted that there is a change. I just append the YYYYmmDD of the agreement to the file name so I can see where exactly the agreement with Apple is changing.

From there, a tool like Kaleidoscope can run a graphical diff on the text if you copy it into a TextEdit document or otherwise get the content out of it's PDF container. Preview will allow you to copy all the text and paste it into a Text Edit document, but I also have a Folder Action created in Automator to convert any PDF file dropped into it's folder into a rich text file and dump the result on my Desktop.