The second trilogy,
The Liveship Traders, follows the Fool around various places, I believe. I've still to read it, but I've heard very good things about it, and it's definitely recommended that it's read.
The third trilogy is the end to the whole saga, sadly. But it's a good end. Everyone who was still alive by the end of the
Farseer Trilogy is in the
Tawny Man Trilogy, including Fitz - who everyone still thinks dead, hence his going around as Tom Badgerlock. And that's all I'm going to tell you.
The third trilogy is a definite must-read, even if just to finish the tale of Fitz. You don't
need to read the second trilogy before starting on the third (I didn't, and I don't think I missed anything important), but if you like Hobb, then goferit.