Make your own - cheaper, and you are in control of the ratios. As someone said, gainers are usually loaded with sugars.
Great recipe, feel free to modify:
1-3 cups skim milk
2-3 scoops Whey Protein
2-4 tbsp Peanut Butter
1-2 cups Fat free yogurt
1-2 cup Oats
1-2 tbsp Olive Oil
That can add up to a lot of calories. If you are a true hardgainer, and have a difficult time putting on weight, this is perfect for you. But just to be safe, keep an eye on the scale. If you're gaining too much, too fast, you need to slow it down a notch.