Whether you're cooking for two or six, a standard cookware set such as the Cuisinart MCP works. (The exception being a small Dutch oven, something about four quarts in size.) But when it comes to bake ware smaller pieces are worth the investment. For example, trying to make a soufflé for two in a 4 quart soufflé dish is asking for disaster.
Soufflés and Ramekins
I recommend purchasing both a set of 1 cup soufflé dishes/ramekins and a 1 quart soufflé dish. You'll use these not only for soufflés, but to make things like mousses, puddings, flans and even casseroles in.
You can choose Corning, Emile Henry, Pyrex or something else. Corning and Pyrex are both glass, but Pyrex is clear glass and promotes browning on the bottom and sides. This may or may not be a good thing depending on what you're cooking and how long it cooks. Emile Henry is clay and the classic French choice is white porcelain.
I have all three and particularly like my Emile Henry pieces. They're quite handsome and so look good on the table and they’ve proven highly durable over the years.
Casseroles and Baking Dishes
Try reducing a casserole recipe from six servings to two or even three and cook it in a 9 x 13 pan and, like the soufflé, you have a disaster. You can do some, perhaps most, casseroles in a soufflé dish, but there are times you want a shallow dish to promote the development of a crust. You probably already have an 8 x 8 baking dish. But consider buying a couple of oval au gratin baking dishes. I find these handy for gratins, of course, but also things like cannelloni or baked baby artichokes.
I also have a two-quart square, lidded casserole that I use for cooking cabbage and frozen vegetables. Your choice of brands for casseroles and baking dishes is the same as for soufflé dishes and ramekins.
Cakes and Pies
Pies are the hardest bake ware to downsize. Very few companies make small pie plates (a 6-inch diameter pan is ideal for two). But I did find some small pie plates at Kitchen Conservatory as well as small cake pans, and baking dishes.
If you're wondering about sizes, I found a chart giving sizes and volumes at CookingVillage.com.