Yes, the post workout shake is of ut-most importance... Consume it RIGHT AFTER your workout. Just as mgoose said, stick to that 2:1 simple carb and fast acting protein ratio. They say fat-free chocolate milk works well too... but i'm not sure, considering milk is a casein.

Mine consists of... based on my weight.

-40g simple hi-glycemic carbs (cran juice or maltodextrin)
-30g whey protein isolate
-20g (1tbsp) Organic Honey
-5g L-glutamine
-5g BCAAs

I also take antioxidants Vitamin E & C (1g of each post workout)