As boring as it will sound text books are great sources. I was always interesting in the why not the how. I'm on mobile and on my lunch break at work but when I get home I will edit this post and tell you the books I studied a lot when I was in and just out of culinary school.
Also I continually use this approach to cooking. I'm still a student, 10 years later. I still want to learn about methods I don't use often as well as ingredients. I go out of my way at home to buy ingredients I never use at work as well as methods. Anything will make you better at what you do and possibly more marketable in your future. Okay be back soon with an edit!
EDIT: Professional Baking, Professional Cooking, and Garde Manger are both great text books that I go back to when I am feeling rusty. This is my Charcuterie Bible