I feed Premium Edge skin and coat formula (it contains salmon  I believe fish is very important to the newfie) and Chicken soup for the dogs soul.   I like to always offer 2 types of dog food in case I get a "bad batch***" bag  my dogs will not be forced to eat it. 
I free feed my dogs, that means there is dry kibble always available for them to nibble on.  I supplement with raw meaty bones ( turkey necks, chicken,venison,fish ect) and table scrapes. Yes ! people food    My dogs enjoy veggies,salad,bread, pizza,tuna ,fruit, an occasional sweet.....   just about anything I eat they eat  (in small amounts!!!)

**** bad batch dog food    sometimes in the processing of dogs food  bacteria  gets in the dog food.   Maybe the machines were not cleaned well,maybe bad ingrediants, or the dog food was not processed correctly     this can result in a very sick  or dead dog.  This happens more often in comercial /cheap dog food  but can happen to any of them.
  Most dogs if given a choice will not eat bad dogfood.  But if its all they have to eat  they will eat it.  

A bit about free feeding. It works great for some newfs. Probaly not for the couch potato newfie. 
Some of the benefits are:  nibbling is much better on the digestive system, reduces the chance of bloat, reduces food agression, you can offer 2 types of kibble,your dog never being hungry and gulping down his food.
All my newfs are raised this way from puppyhood... It works well for my newfs but  if  you try this , moniter his weight closley and if your newf gains weight  he needs more exersize or maybe he is just to much of a food hound for this way

Start reading  the ingredients  it should read like  a good soup or stew.  This is an example of good ingredients (premiun Edge skin and coat):   salmon, salmon meal, potatoes, cracked barley, whole grain brown rice, egg,flax seed, kelp, carrots, peas, tomatoes, apples, cranberry, rosemary and then a list of vitamins

Quality Foods Should Contain:
Superior sources of protein, either whole fresh meats or single source meat meal (ex. chicken meal rather than poultry meal)
A whole-meat source as one of the first two ingredients.
Whole, unprocessed grains, vegetables, and other foods.  Nutrients and enzymes are more likely to be found in unprocessed foods.

Quality foods should contain a MINIMUM of the following:
Food fragments - lower-cost by-products of another food manufacturing process, such as brewer's rice and wheat bran...Manufacturers usually include at least one fragment to help lower costs. Beware any food that includes several fragments.
Meat by-products (not handled as carefully as whole meat) - any food that contains meat by-products as the MAJOR protein source indicates a low-quality product.  
Fats or proteins named generically (ex. animal fat/poultry fat instead of  beef fat/ lamb meal)
Artificial preservatives (BHA, BHT, ethoxyquin)
Artificial colors.
Sweeteners (corn syrup, sucrose, ammoniated glycyrrhizin) to improve unappealing food
Propylene glycol - a toxic substance when consumed in large amounts; added to some "chewy" foods to keep them moist.

******* the underlined products I have used personaly and had good results.
Abady   This is highly recomended by Kloof Bears newfoundlands
Azmira Tucson, AZ 8%  "...uses many herbs, chelated minerals, extra vit. C; combination of beef and fish is nice."
Back to Basics Beowulf Natural Feeds
Syracuse, NY
19%  "Human grade & hormone-free ingredients. Delivered fresh from manufacturer....Very high fat content (19%) reflects company owner's philosophy that more fat is good for dogs.  Also offers a pork-based formula."
Best In Show Power Food Jupiter, FL 15%  "We love seeing two meats in the top two places; also makes a super-high protein formula and a lower-fat version." 
Canidae San Luis Obispo, CA 14.5%  "Three major proteins in the top five ingredients: that's a good food!"
Eagle Pack Holistic Select Mishawaka, IN 15% "Not all Eagle products are this nice; the Holistic line is their best; inclusion of any organic ingredients is a nice touch."
Flint River Dry Water Riverside, CA 10%  "Intends water to be added. Sold by independents and shipped direct."

Natural Balance Ultra Premium Pacoima, CA 13%  "Three proteins in top four ingredients. Worth the effort to find." 
Pinnacle (Breeder's Choice) Irwindale, CA 15%  "Like Eagle's food, this food is the best offering from Breeder's Choice. We'd prefer they use whole veggies. Still, nice food." 
Prime Life Oxford, CT 16%  "Two proteins in top two spots. All grains ground whole. "We don't like seeing "flavors" even if they "natural."
Solid Gold El Cajon, CA 12%  "Does not use animal fats, only healthiest oils. This formula also lacks foods many dogs are intolerant of/allergic to."
Showbound Naturals (Integrated Pet Foods) Exton, PA 14%  "We prefer this food to the "Lick Your Chops Line."
Timberwolf Organics Center Hill, FL 18% "Newish company, great products. Maker ships fresh."
Wellness Fish and Potato Lowell, MA 12%  "We chose fish-based food for dogs who are allergic to other proteins. Other Wellness foods are nice, too. Food tends to be super-dry."
Back to Basics (Chicken Formula)       Back to Basics (chicken)
Best In Show "Solutions"   Best In Show "Power Food"
California Natural   California Natural    California Natural 
Innovative Vet. Diets Duck/Potato         
Wellness Super5Mix Hormone-Free Lamb   Wellness Super5
Wysong      Wysong Maint.