One of the first things I always talk to my clients about is post workout nutrition. You have just spent an hour or so working hard, so why waste it. Post workout nutrition is a vital part of the of the total health equation. Do it right, and you can see significant gains in lean body mass, do it wrong, and you can stagnate. After telling this two my clients, I usually get two questions, "What should I eat?" and, "When?" Lets Take a look at both of these.
"What should I eat?" This is the first and more complicated of the common post workout nutrition questions I get. The most simple answer, is milk. Milk has a great protein make-up, containing all essential amino acids your body needs to refuel. It also has a good amount of carbohydrate, the approximate ratio to protein is 2:1. 8-12 oz of milk after a workout should do the trick. Many studies have covered this topic (including this one) so I feel milk is the best option for the general public. Here's the tricky part, many people (especially females) don't like milk. For those who don't like milk, whey protein powder provides many of the same benefits (sometimes more as you have more control over the fat and carb content) however, I typically find those who don't drink milk don't like whey protein either. Nuts are another option, though they are not as complete as milk or whey. Eggs are great if your stomach can handle them. The important thing here is to get a complete source of protein along with a few carbs and some fat. Remember though that protein takes more water than other nutrients to breakdown, so continue to hydrate post workout.
So now we come to the question of "When?" This subject is up for debate, with time frames ranging from immediately to 1 hr or more after the conclusion of resistance training. as a trainer, my stance on the subject is lax. Many of these studies discuss optimal timing. Most people looking to generally fit do not need an optimal time, but rather a general one. I tell clients to eat as soon as they can. This usually puts them in the 0-60min range which is the debated time frame. This means that while they may not get maximum benefits, they will close to it. Though I do not know the source study, I was always told in physiology that within 20 min of exercise provided the most benefits, for what it is worth.
So in short conclusion, drink milk asap after a workout!