The op amp section in the Elements page developed by Prof. Mastascusa provides a good explanation of op amps.
You may also be interested to read
the following page on history, properties, and applications op amps:
http://www.eng.usf.edu/~saddow/eel3302/741.html
Chapter 5: 43 and 46.
Chapter 6: 1, 3, 14, 17, 20,and 39.
Thank you.