http://en.wikipedia.org/wiki/Tales_of_Dunk_and_Egg

I just finished the first one (The Hedge Knight), it's good stuff, I like the self-contained nature of the story, and there are no cliffhangers by the time it's over. It's set 90 years or so before the events of the main series. There is a very minor link between the two, if you've read the 4th book you might already know what it is...