This is a nifty list. However while not free nor digital, my approach is to buy earlier editions of standard texts from Amazon. The reason I suggest this appro

This is a nifty list. However while not free nor digital, my approach is to buy earlier editions of standard texts from Amazon. The reason I suggest this approach is that I compared the Biochemistry book in this list against my preferred text, and in my individual case the 9 or dollars for a Stryer 3rd Edition is more than worth the price differential.