I finally got my hands on a cast-iron skillet, and I believe I've fallen in love. I will keep my non-stick skillet on hand for dry-frying tofu or scrambling eggs (do not try this with a cast iron skillet without a ton of oil), but there is no going back otherwise.
Coconut oil: more like butter, really, since it's solid at room temperature; I like it because it's suited to high temperatures and contributes no flavors to a dish. This was demonized by many medical professionals because it is high in saturated fat. However, since the trans-fat epiphany, it's become clear that not all fats within the same category are equal - saturated fat from plants is, in fact, quite healthy, as long as it is within moderation. Medium-chain fatty acids, ahoy!
Dubliner cheese: and Kerrygold cheese, in general. I love strong cheeses but these aged cheddars are pretty damn awesome.
Yukon gold potatoes: for everything other than a loaded baked potato (for which Russets are king), these are amazing and healthy - high in minerals and vitamins.
Cinnamon: in my coffee. It's anti-inflammatory, high-fiber, anti-microbial, and it controls blood sugar, the latter of which is perfect to have with a meal.
Ginger: mixed in my Greek yogurt with molasses, flax, walnuts, and pecans. Ginger has way too many health benefits to pass up, and it lends a little sweetness and spice.