Ronald Reagan mac and cheese uses an egg [0].
I haven't tried it, but molecular gastronomists (or are they modernists?) use sodium citrate to keep real cheese creamy when it's heated [1].
0. http://lincolnslunch.blogspot.com/2012/02/ronald-reagan-maca...
1. http://modernistcuisine.com/recipes/silky-smooth-macaroni-an...
I typically make a roux, add a sharp/extra sharp cheddar to it to make a very tangy cheese sauce, then stir in the cooked macaroni, and a touch of paprika and cayenne and sprinkle breadcrumbs on top. Sometimes I will add feta or a little blue cheese if I have any on hand. My Midwestern wife adds Velveeta since she likes the extra creaminess and it's how her mom made it. Either way is fine with me.