First an fyi. Velveeta and american are not "cheese," they are cheese food.
For a creamy mac&cheese with flavor it helps to start with a bechamel sauce. Essentially, butter (or other fat) and flour cooked together, then slowly adding milk until you have a white sauce. The grated cheese is added to this.
For cheese, choose cheese with flavor. Use sharp cheddar instead of medium. If you want to pump it up, add gruyere for a little tang. Other good cheeses are parmesan or fontina (or american equivalents).
I use Martha Stewart's recipe (link follows), but you really don't have to go that far. You can just make the bechamel/cheese sauce, throw it on the pasta, and you're done. Also, if you use MS's recipe, it makes a LOT. Cut it in half if you're not feeding a huge crowd.
http://smittenkitchen.com/blog/2008/05/marthas-macaroni-a...