A great reference manual is the
B737 Cockpit Companion by Bill Bulfer. He also has a
737 app that is essentially a ipad version of the book. Unless you think you may fly the classic, just get the NG version.
Someone has put a
scanned copy online to see what you get. There isn't a lot of "fluff", but the it is very clever and it lists everything by panel, then with added system description. Do Bill a favour and buy the book if it helps you.