My husband is thin too. The MD said the Peg has made a big difference for folks in maintaining a reasonable weight. He doesn't have it yet so others will have to tell you more about that.

There is carnation 560 that is loaded with calories. He tolerates it well but I read here that someone compared it to Elmers glue so I'm guessing the taste is not so great to some. And it's not cheap.

The dietician also recommended going to GNC. There are several products that have up to 2000 calories of this powder mixed with 16 oz of water.
We had never been to a GNC before and in our area at least it was filled with bodybuilders. I was betting those kids were wondering what us old folks were doing there...

Dave said that was also "ok."