A post workout shake is important but remember what you eat for the next meal AND breakfast is just as important if not more. So protein to bed, protein to rise.
As far as whats in your shake/meal you want a fast acting protein (like whey) a high carb source to re-fuel your muscle glycogen and a lil of good fat like flax oil, fish oil, natural peanut butter so on.
For example my post workout shake has Banana, strawberries, natural peanut butter, whey protein, carb free protein pre-made shake (use that for lil flavoring since its choc and oatmeal. This post workout feels great and gets all needed requirements and is damn tasty too. However My next meal that comes I make sure has great protein and make sure to get in a protein source that next morning as well.