Good quality dog food

Question
We collected our little rescue dog last Friday. He is a gorgeous little boy, but definitely underweight. Since it is so cold at the moment I'd like to feed him with a good quality dry dog food, to help bulk him up. He is still quite young, the humane society think he'd about a year. He's going for his vet check this Thursday and I'm hoping he can give us a closer idea of his age. He was neutered on the day we collected him. He is a very happy, affectionate little guy but I would like to feed him right. He was advertised as a terrier mix at the humane society, he looks a bit like a small tibetan terrier/shih tzu mix and he weighed 145lbs when he left the society. Thank you for any help.

Answer
What was the shelter feeding?  There is nothing wrong with most of the common brands of dog chow.  Much of what you read is marketing hype put out by those selling the more expensive chows.  Most of my experience is with Pro Plan, but I know Purina's other grades are fine as well as Iams and Eukanuba.  So if the shelter was feeding any common brand, you may as well stick to it.  Most dogs will thrive on most chows. Changing chows is more likely to cause problems than prevent them.  If you do change, Science from the vet is another good option.  

145 pounds, perhaps you left out the decimal point?  Be careful not to over do bulking him up.  A few extra pounds on a small dog is very hard on it.  Your dog definitely should be narrower at the waist than the hips and chest.
You should be able to easily feel the ribs, but not see them.  Each dog is
different.  Standard recommendations are a good place to start, but each dog
must have its food adjusted to its individual needs. Here is a link to a good illustrated guide,
http://www.longliveyourdog.com/twoplus/RateYourDog.aspx