I feel quite comfortable playing pre flop, but I feel that I am weak in post flop play. I lack the big picture of post flop play.
Can anyone give me a good reference for post flop play?
No Limit Hold'em Theory and Practice is the textbook on this subject, and it would be the place I would start reading first.
As well as the link Toby has suggested above take a look a the following:
The last one is a quiz. There are a lot of useful quizzes on this site. If you dont already have an account I would recommend that you sign up and give some of them a go.
Hope some of these links are useful