The best source is your vet. My vet gave me a list of recommended brand dog foods.
I use Wellness for my dog -- it is considered a very good quality food. It is not cheap, but it is considered very good quality. But as my vet explained if you feed them better your vet bills will be less and they will be healthier.
You should have found out though what he was eating before as it can cause problems for the dog to change their diet - you should do part their old food and part their new and then increase the amount of new until that is all they are eating.