I have recently started reading Knight: The Medieval Warrior's (Unofficial) Manual by Michael Prestwich. I am relatively new to researching the medieval era and really like this book so far. It takes a look about knightly life from a historical standpoint using a multitude of resources. It does not solely look at the life of a knight based upon romances that were written at the time, though it does take these into account.
It is written as if it was a manual for the aspiring knight and seems to have a lot of good information that is broken down in a way that is easy to understand. It will be a good spring board for further reading to develop my knowledge of the period. The author seems to have written a wide variety of books specializing in this era and I would recommend this to anyone looking to obtain a foundation of what life was like as a knight during the 14th and 15th century. It's only about 18 dollars on Amazon.