How To Gain Weight Fast
Fast weight gain is hard to accomplish without the aid of some sort of supplement, but there are several pretty healthy supplements that you can buy to do it. These include a variety of protein shakes made by a number of different companies. The best one for price is Naturade. It costs about a dollar a serving and adds about 900 calories per day. Another quick one, and one that claims to be the best, is Universal Nutritiion's Gain Fast which says to only use it every other month to help your body recover from gaining 5 pounds a week. I would suggest not using this one unless you seriously need to bulk up fast.
Fast Weight Gain Shakes
If you are looking at fast gaining shakes, then you should check out the website by NexTag. This has a list of good weight gaining shakes and has information on several of them to help you choose which one is the best for you. They are each fairly similar to one another, so choose based on price, flavor, or cost per day. This will hopefully get you the most for your money.
Other Ways
If you want to really gain weight quickly, you can try eating at night as well as drinking the protein shake. However, this messes with your body's ability to digest it, which causes it to turn into fat. If this is not the way you want to gain weight, then try the shakes instead.
Problems With Gaining Weight Fast
Gaining weight quickly can through your body into shock, causing your metabolism to speed up sharply, or cause your heart to have to work harder instead of gradually adjusting to the weight. This is rough on your body and could take some time off of your life. I would not try to gain weight excessively fast unless it is necessary.