I don't want to repeat everything others have written on here, though I concur with a lot of it. I will just reiterate a few that I find I constantly use...and add a couple more.
Rice (basmati and brown)
Couscous (love how fast it cooks)
canned tomatoes (all types)
herbs and spices, spices, spices...seriously, I use all sorts, and buy a better quality for a lower price by getting them in the bulk section at places like Whole Foods. Plus, I buy in moderation vs. big bottles so they never sit around and go stale. Also, consider just growing your own herbs...dried are okay, but nothing like fresh herbs.
Big boxes of organic chicken stock -- get a group of these for a good price at costco
Fresh ginger -- dry or bottled is NOT the same. And it will last a while.
Fresh garlic
Fresh onions (again, powdered or dried are not the same. And onions actually have some good health qualities)
Sriracha and/or Chili Garlic -- I have found a number of recipes this perks up
Fish Sauce, Oyster Sauce and Soy Sauce (regular and low sodium) -- like Sriracha, not just for Asian food or stir fry. Great for marinades, and soy sauce is also a good way to add a little something extra
Good quality sea salt -- you can really ruin a good recipe trying to sub table salt for sea salt. And there's really no better way to serve a fresh tomato
Real cream -- probably sounds counterintuitive to "healthy", but just a dash isn't a killer in a large pan of sauce/soup and can give that little something extra.
bread flour -- I just don't think all-purpose is an okay substitute for certain breads and pizza dough
instant yeast
corn meal -- breads, breadings, dusting bottom of pizza crust
saltines -- not so wholesome, but instead of buying chips or cheesey crackers, I just spread some cream cheese or peanut butter on these and a) save money and b) limit my consumption of questionable ingredients
popcorn
Almonds (snacking and recipes)
dried linguini -- boxes and boxes of it

my favorite noodle for stir fry and Italian
panko crumbs -- crunchy breading or topping without the frying.
Little bottles of white wine -- sure, not great quality, but easy to grab for recipes without cracking open a whole bottle (let's face it...I know I can freeze leftovers, but if I open a bottle there won't BE any leftovers

)
Perishable, but I like to keep a block of quality parmesan and some Feta (good with seafood, in pasta cold and hot, in salads, or melted inside a pita). Pre-grated parm is NOT even close in a recipe.
And b/c I'm a southern girl I always keep some frozen okra in the freezer -- except I oven fry mine (which is a little heretical, I know

). But it's one of teh few frozen veggies I like, and DH LOOOOVES it.
We also keep frozen edamame for snacks
