This is probably not the answer you are looking for, but last year I read an awesome book called "Drive" by Daniel Pink. It is about what motivates us (and employees). Might sound boring, but it is an easy read. As a quick summary:
- the carrot and stick approach (e.g. bonus payments) often doesn't work
- research shows that three things motivate us: autonomy, purpose, mastery
I know it sounds all touchy-feely and not concrete "what to do" info, but there's lots of examples and actual research in the book. I encourage you to check it out. It certainly changed my thinking.