Doesn't work unless you're eating it right away, but my favorite mac & cheese is to cook the pasta (rotini, shells, bowties or elbows all work well - shells maybe the best), drain.
Now off heat, add a chunk of real butter (margarine works OK but flavor's not nearly as good), quickly toss to coat all the pasta, add a generous amount of cheese - I like sharp cheddar, but colby, co-jack, other cheddars, Mexican blend all work OK - and a blop of sour cream (low fat or even fat-free works OK), toss everything with a fork until cheese is all melted and sour cream is blended in. Salt (preferrably sea salt) and freshly ground black pepper to taste.
The sour cream blends with the butter and cheese to make a clinging sauce, but it separates somewhat if you try to reheat. So, only cook as much as you'll use right then.
Sorry the amounts are so vague, but I just throw it together. If making a bunch, I use a pound box of pasta, at least 8 oz. of cheese (usually twice that
), 1-2 T. butter, and about 2 T. sour cream. I just eyeball it if just making enough for myself, though. I often cook some frozen broccoli in with the pasta and make that a complete quickie meal for myself.
Sairis' SmittenKitchen recipe sounds very much like what I fix if I need to take it somewhere or need to be able to later reheat it.