From a seasoned Hard Gainer:
Ultimately, I had to make peace with the body I have, and give up on the body I want. Several years ago, determined to gain, I put myself on a program where I was eating constantly, and managed to put on ten pounds. I gave it up because it was costing a lot, and also because I just got tired of putting food in my mouth every twenty minutes.
As I've gotten older, my metabolism has slowed down some (Oh. and I'm drinking less Starbucks), so these days I'm in around where I was back during my Must Gain Weight period.
But I will share my Top Secret Gainer Protein Shake recipe:
In a blender, combine:
Two cups NOT low-fat vanilla yogurt
One raw egg (I laugh in the face of death! And Salmonela!)
One pack Alba non-fat dry milk (stuff is cheap and loaded with protein)
Something to flavor it (peaches, strawberries, blueberries, or my favorite: Ovaltine)
It's like 50 g of protein, Yo.
(Your body can't ever assimilate more than about 40 g. protein per meal, no matter who you are, so you're just pooping it out if you're going over that.)
I avoid supplements--because I think they're a waste of money--and go for whole foods, most of which I fix myself.
In the supermarket, look for Barilla Enriched Pasta products: it's Pasta with extra protein added!
Another favorite of mine is Odwalla Pure Protein. They charge an arm and a leg, but it's whey protein and a banana, an orange, and an apple, and it tastes dandy.