For a truly creamy mac and cheese dish, you'll want to include one or more great melting cheeses (in addition to a cheese for flavor like extra sharp cheddar cheese.) Substitute real cream for all or part of the milk in the recipe, and try cooking the noodles in milk rather than water.
A creamy mac and cheese recipe starts with cheeses that are excellent melters. Varieties like swiss, muenster, fontina, mozzarella, and Monterey Jack are excellent choices. Soft cheeses like mascarpone, cream cheese, and cottage cheese can take creaminess to another level.