Alrighty I may be in the same boat as you, I have a tough time putting on weight (unless I eat crap, but I eat pretty healthy).
I would recommend Optimum Nutrition Pro Complex Gainer - 1 serving has about 700 calories, 60 grams of protein. The protein in this blend is a slower absorbing protein good for taking about an hour or 2 before bed so you can break it down as you sleep. I usually make two shakes of this a day. One of which I take as my last meal of the day about an hour b4 bed.
I also take Optimum Nutrition Gold Standard Whey Protein. I use this faster absorbing protein as a post workout shake.
My goal is to take in atleast 200 grams of protein a day but I prefer to get 300 grams. 1.5 grams per pound....
Now I realize you say you dont want to take creatine or many other supplements but I will just let you know what I have had good results with.
In my postwork out shake I take glutamine, creatine, with my protein.
I also make my shakes with pasturized egg whites and milk....makes them alot tastier...
I also take CLA and fishoil gel capsules with dinner.
My goals may be different than yours but I am attempting to gain 30 pounds of muscle. I am 190 and want to get to 220. Last time I was into lifting I made it to 215 but then went to basic training and came back 178 pounds.
but if you want some decent info on creatine try
http://www.absolute-creatine.com/ if i spelt that wrong just google it...i got that link off these forums about 6 years ago...good info there.