Earlier in my career, I worked for years in cookware stores. Suffice it to say I have a lot of cookware, yet out of the shelves of equipment in the kitchen, there's a handful of tools, pots and pans I turn to over and over again. They're so essential when cooking for the two of us that I've got duplicates of almost all of them - just in case the original breaks or gets damaged. While I'm not tied to any particular brands or exact styles, these are the pieces of equipment I find indispensable in cooking for two. The best part is that they don't have to be expensive.
Of all the saucepans in my kitchen, the ones that get the most use are the smallest - a .75-quart, a 1-quart and a 1.3-quart. Trying to make sauce for two or a small amount of rice or other grains is virtually impossible in a 2- or 3-quart pan, but these smaller sizes are perfect for all kinds of tasks. The good news is that many cookware manufacturers will offer small saucepans for very good prices as a way to get you to try their products, so you should find a wide selection of good quality pieces priced from $20 to $50. (A lid is nice but not absolutely essential - it will add to the price, and a small plate can stand in if necessary.)
Toaster oven-sized "broiler pan"
This two-piece tool looks like a tiny sheet pan or roasting pan with a rack that fits on top. With the rack, it's invaluable for salting and resting steaks and chops or broiling garlic bread or fish. Without the rack, you can use it to roast a couple of servings of vegetables like green beans or asparagus or bake a couple of biscuits. For around $15, this set is such a bargain you'll want two. (Another slightly larger and more expensive option is a "quarter sheet pan" -- a 9x13-inch rimmed baking sheet -- with a rack, although it can be difficult to find a rack that fits this size.)
Mini food processor or chopper
A full-size food processor, while great for larger recipes, is often too big to process small amounts of food. But a mini sized one can make a small batch of pesto, puree a couple of servings of soup or sauce, or mix pasta or pastry dough for two. Cuisinart and Kitchenaid both produce these small machines. Or, if you already have a large food processor, see if the manufacturer offers a small bowl that fits inside the large one. Depending on the size and brand, you should be able to find something for under $40.
Large medium-mesh strainer
While a colander works great for draining pasta or blanched vegetables, it's often overkill for small batches. I use a large strainer for almost all these kinds of jobs - it works great for two servings of pasta or vegetables, and it's perfect for straining tomatoes, sauce or soup. Plus, it's easier to clean (mine is dishwasher safe, and it fits better than the bulky colander) and at about $15, much cheaper.
Small glass or ceramic baking dish
I have half a dozen of these in various sizes (they were a favorite staff giveaway at the cookware stores) and at least one is virtually always in use. Not only do we use them for baking casseroles or gratins for two, but they're also great for marinating fish or chicken and breading foods to be fried. The oval shapes I have range from about 7 to 9 inches lengthwise; I find them to be the most useful sizes. While you can spend a lot on French ceramic dishes, you can also find a good selection in the $15 to $20 range.
Eight-inch cast iron skillet
This little workhorse practically lives on the stovetop in our kitchen. It holds two chicken thighs for braising or frying; it's the perfect size for heating corn or flour tortillas for tacos; it's just right for a small batch of cornbread; and we even use it for desserts, from simple fruit crisps to upside-down cake. Cast iron is available pre-seasoned and at less than $15, it's a deal you shouldn't pass up.