You caught my attention with the Middle Ages books talk. So I just looked up Sharon Kay Penman on Amazon and all her books have pretty good ratings and look really good. Did you co-worker recommend any special ones? Or have you read any of her books in particular you would recommend to start with?
I decided to go with the Plantagenet series so the first book I read by her was "When Christ and His Saints Slept" and have since moved on to "Time and Chance" which I am in the middle of.
I think you will like them.