It cooks up like spinach, but the leaves have a more earthy taste, more like beet greens. Many recipes cut the thick stems away from the leaves, since the latter cook more quickly. Cut up the stems and saute first, then add the leaves. Rainbow chard, with its colorful stems, is especially pretty, but green chard tastes just as good. Blanched and drained, with the water squeezed out, you can use it in any recipe where you'd use cooked spinach. It's easy to grow as a fall vegetable, too, as it prefers cool weather.

"Swiss chard is not only one of the most popular vegetables along the Mediterranean but it is one of the most nutritious vegetables around and ranks second only to spinach following our analysis of the total nutrient-richness of the World's Healthiest vegetables." So says Whole Foods. Chard has a wonderful flavor and holds up much better than spinach.
Food52 has some amazing chard recipes - just plug in chard in the search recipes section.
The NY Times also has some great recipes http://topics.nytimes.com/top/news/health/series/recipes_for_health/chard/index.html