Digital scale: People of the world: bake by weight. It is our true calling. We might use this baby more than any other tool in the kitchen. It makes measuring easy and precise, and you avoid having to clean 10 different measuring cups and spoons. My baking improved immeasurably when I began weighing ingredients, because it takes a lot of the guesswork out of measuring things like flour, nuts, sugar, etc. Our Salter model is not available online, but this one comes highly recommended. Definitely get a scale that tares and switches between ounces and grams; also make sure it measures in 1-gram/.05 ounce increments.
Nice measuring cups/spoons: Yes, I just finished saying that measuring by weight > measuring by volume, but we still use measuring cups for certain things. These All-Clad measuring cups/spoons are like the heirloom Rolexes of the measuring cup world; they gleam and feel nice in your hand and don't get dinged up in the dishwasher. My dad bought these for Mark's birthday and literally every time I use them, I'm like, man these are some sweet measuring cups. That's the mark of a good gift, no?
Cake stands: Cake stands make a particularly nice gift for people who like to bake or host parties, where they can hold anything from cakes to tarts to, I don't know, sushi rolls. If you do a search on Etsy or Ebay or Replacements, you'll find hundreds of cake stands, from pink depression glass to pale green jadeite to lacy milk glass. I found the best deal on mine, the white milk glass number pictured below, on Ebay. The same stand can be found here.
Salt cellar: It's handy to keep a container filled with kosher salt by the stove for cooking. We have this one, which holds enough salt that we don't have to refill it more than once a month. I also like this one.
Enameled cast iron French oven: If I were rich, I'd buy all my friends one of these. They are lovely to cook in: they heat evenly, retain heat well and have this nice enamel surface that is kind of nonstick but produces lots of fond (caramelized bits that appear after good searing). I'm partial to Le Creuset because of their truly excellent warranty, but Staub/Emile Henry and even Kirkland (Costco) make nice looking ones. 5.5 quarts is a good size: it is big enough to braise a double batch of ragu bolognese, bake a loaf of bread (just remember to unscrew the top if you put it in the oven!), sear/roast a fat pork tenderloin and simmer soup for 8.
Chef's knife: I think you can get away with having one good chef's knife, one sharp paring knife and one serrated bread knife. The chef's knife, for me, is most crucial. The most important thing is how the knife feels in your hand and how sharp it is. From there, it's all about how much you want to spend. We like Shun knives best.
Ramekins: For souffles, puddings, creme brulee, individual gratins and for setting out nibbles at parties. We have these but I don't think there's any need to spend so much. I got these for my sister last year.
Silicon baking mats: Technically, you can get through life with baking mats, but their nonstick/heat resistant properties provide a good surface for kneading dough or rolling pie crust or for baking cookies or whatever. We have two and use them constantly.
Essential cook's tools: Microplane grater (hooray for grating ginger, citrus zest, hard cheeses without grating your knuckles raw at the same time). Locking tongs. Silicon spatulas. Wooden spoons and spatulas. Bench scraper.
Pizza stone: If you want to make good bread/pizza in a home oven, you need your oven to get really hot and to stay hot. You need a pizza stone. (I've heard some people use unglazed tiles from hardware stores, but I was slightly concerned about chemicals that might be present in tiles.)
Kitchenaid stand mixer: Our kitchen workhorse. If you want to know if we're home, listen for a whirring sound. If you don't do a lot of baking, or if your baking repertoire doesn't include heavy-duty tasks like brioche kneading, you probably don't need one. Also, if space is a concern in your kitchen, it probably isn't the best option; you can make dough with other tools, like a hand mixer and, you know, your actual hands. But if you do a lot of baking (like, more than twice per week) and if that baking includes dough making, by all means get a stand mixer. It makes routine tasks much easier and makes certain recipes, like brioche, attainable.
Cookware: We love our wok, which is heavy-duty, well seasoned carbon steel. Ours looks a lot like this one, but it was a gift from my best friend Julia so I'm not sure. Stay away from stainless steel or lightweight woks with nonstick coating. We cook bacon and steaks in a cast iron skillet and eggs in a nonstick pan. We have a set of heavy/tri-ply pots and pans for almost everything else. Everything but the wok and the cast iron skillets conduct heat unevenly, so they're not perfect but they work for now.
Bakeware: I don't really have any specific recommendations except, if you bake a lot, to get pro-grade heavy baking sheets that won't warp in oven heat. We have these Chicago metallic sheet pans and these cake pans, which seem to be holding up well. We use an old, beat up (no name) loaf pan for bread because it heats evenly. Our Le Creuset stoneware loaf pan is super pretty but sticks a bit.
Dish towels: Every gift guide seems to have a bright, graphic tea towel on the list. There are many pretty towels out there but I can't bring myself to spend $$$ on a towel I know I'll spill chocolate sauce on. That's why I like these linens from Ikea (these and these), which are cheerful, cheap and eminently replaceable. They double as pot holders and, if my linen napkins are all in the wash, I'll set out kitchen towels instead. (I do like this Pride and Prejudice "in vain I have struggled" dish towel though.)
Food Books:Mark's favorite food book is Harold McGee's On Food and Cooking. If you have ever been to our house, Mark has probably pulled out this book at some point to settle a food science debate, like "why does fish smell?" Definitely good for food geeks, but it is also a legitimately useful resource.
Mark's go-to bread baking books are by Peter Reinhart's Bread Baker's Apprentice (we like his pain a l'ancienne and his pizza dough) and Rose Levy Berenbaum's Bread Bible (we like her rye, pumpernickel, hearth bread and flax seed bread). We also use Dorie Greenspan's Baking book, which includes a wide variety of desserts. The only bad thing is that she doesn't include weight measurements, but her recipes are great.
I really, really love Nigel Slater's food writing, particularly Kitchen Diaries -- the photography is super appealing and I love his perspective on cooking seasonally. Plus, he's not afraid to admit that he buys frozen chips sometimes. He is probably my favorite food writer, actually.
(I'm not sure I can suggest a go-to cookbook. I basically taught myself to cook using Mark Bittman's The Best Recipes in the World but, now that I consider myself a confident/fairly skilled cook, I don't think I would recommend it to beginning cooks. The good: he makes complex recipes/ingredients accessible and some of his recipes have become total staples for us -- shrimp with parsley and garlic, two way chicken, his general technique for enchilada chile sauce. The salad section and the pasta sections are useful, too. The bad: the instructions are often vague and many of the recipes don't really work (do not recommend his biryani, for instance). I learned a lot, but more because I was motivated to become better and not necessarily because of the cookbook.)
Food: I am a big fan of homemade food gifts. Mark's parents send us batches of homemade jams and sour cherries they put up each summer. I've also received platters of cookies and jars of spiced pecans and biscotti. The only hard thing is finding pretty containers. For cookies or biscotti, I like these jars from Ikea, along with bakers twine or nice ribbon and a card listing all the ingredients. Mason jars are always handy, too. If you are giving liquids, these bottles from Ikea are excellent. And for platters or bowls, I like old silver platters or milk glass candy dish, both of which I often see at thrift stores for not much money.