What to grow on one acre of land depends on a wide array of conditions, including, but by no means limited to, location (you're unlikely to grow the same crop in New York, for example, as you will in Montana), weather, soil type, labor, transportation and marketing. Growing crops for personal consumption is a different proposition from growing crops for sale. There are crops, however, that can maximize the potential of a single acre.
If your goal is to sell what you grow at a roadside stand or at your local farmers' market, then a variety of common, and popular, vegetables can be profitably grown on an acre. 100 stalks of sweet corn, for example, will commonly produce between 200 and 300 ears. Lettuce, cucumbers and green beans are all high-yield crops, and garlic offers the advantage of being valuable without requiring inordinate labor.
Strawberries, raspberries and blueberries are all high-value crops that require relatively little ground. They can be expensive crops at start-up, however, and are labor-intensive. Expect at least one year, and probably two, before berries reach a profitable level of production.
Cut flowers combine beauty with profitability over an extended growing season. Among many others, tulips, daffodils and lilacs arrive with the spring, although it's worth noting that, because the blossoms grow on long-lived and slow-growing bushes, lilacs are not an overnight project. Roses and chrysanthemums are common summer blooms. Even autumn provides opportunities for growers of such blooms as iris, poppies and freesia.
Just as you'd be unwise to place all of your investment dollars into a single stock, you'll be equally unwise to dedicate your entire acre to a single crop. Weather that doesn't trouble one crop may severely retard the growth of another. Market conditions can vary wildly from year to year. The hired help you count on for one season might be unavailable the next. Even on a plot of ground as small as an acre, diversification can help protect you when one crop fails or becomes unprofitable.