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Velveeta all the way. And my mom always puts large canned whole tomatoes on the top before baking it - the acidity from the tomatoes cuts through the overwhelming velveetyness.

Cheddar, Gruyere (or Fontina), and Paremesean (usually around 40/40/20) for the roux/sauce, then a mix of 50/50 cheddar/parmesean for the topping. Why use bread crumbs when you can use more cheese.

As for bacon, why not. Bacon makes everything better. If you have moral opposition to swine and are coming to my house...well, 1) You're coming to the wrong house, but 2) My solution would probably be to make two 9x13 trays, one with and one without.

and eventually i'll add spell-checker as well

I'm fine with just about any cheese combo, including the evil Velveeta, béchamel or not, so long as there are NO BREADCRUMBS!!!

Last night I used sharp cheddar and monterey jack. I made the skillet mac and cheese from the new Cook's Country issue. It came out really good and it was very easy to put together. I like sharper cheeses. Last night I used less than the recipe asked for and it came out very cheesy and delicious.

Bechamel/Parmesan is how I often like the sauce. Simplistic, maybe. No bacon. Sometimes stewed tomatoes on the side to compliment the tang. Added some shredded Manouri on top last timed and baked it. Good.

Manchego is a great idea. Will try it.

50% Sharp Cheddar and 50% Monterey Jack - got my recipe from The New Best Recipe and it's the best I've had.

In addition to cheddar, Velveeta, and possibly a domestic Gruyere, lately I've been adding some Butterkase.
http://tinyurl.com/2nn2x5

My current preferred mac and cheese recipe is located here:

http://www.epicurious.com/recipes/food/views/102738

Very creamy, with just enough punch from the chipotle. (Do not let the amount of sauce that it makes scare you, just go with it.) Making your own bread crumbs is essential. This recipe uses only cheddar and we usually get some Irish cheddar from Trader Joe's. However, on reading the comments above, I think we will add some gruyere the next time we make it for a little change!

If it's macaroni and it's got cheese (or some rendering thereof) on it, I'll probably eat it. Reared on the Blue Box, no snob am I. However, I have found that a little hit of blue can add pleasant dimension - a boost of tang and salt, with perhaps a touch of sweet.

Ideal: government cheese; failing that Velveeta, both combined with Extra Sharp cheddar and skinned knuckles.

M&C is my favorite method of using up all the little random odds n' ends of cheese languishing in my fridge. If necessary, I'll use cream cheese or plain yogurt as a binder, and adjust the spices to suit whatever the creation is trying to be. I honestly don't find the idea of binding myself to a M&C recipe appealing - it ruins the fun of reinventing it every time I make it. I realize that's a luxury, however - if I had other people to cook for besides myself, they would probably want some consistency.

One thing I always love to do, however, is to add some corn and peas to counterbalance all the salty, cheesy numminess :-).

I love using DeCecco orecchiette. Those little ears soak up the sauce, don't cost much more than elbow and their concave sides acts like bowls for the cheese sauce.
You do need a little bechamel to melt the sharp cheddar evenly & keep it from clumping on the macaroni. I use 1/4 cup of flour with an equal amount of melted unsalted butter & cook it til it's smooth & nutty smelling.
Gotta add 1 tbsp. dijon, a pinch of white sichuan pepper & salt & stir that in well. Then slowly add the milk (for a total of 24-32 ounces depending on how thick you like it, I used 20 oz. of nonfat milk yesterday & it was great), whisking it in over low heat until the sauce is smooth & creamy.
When the sauce is smooth & thick, I add 16 oz. grated sharp cheddar (cracker barrel is fine, this is not the place to use an artisan cheddar from Britain) stirring in a little at a time into the bechamel sauce, keeping it over low heat, until the cheese is fully incorporated & fondue-like.
Then I add the cooked pasta to the cheese sauce pot (about 12 oz dry), stir it well & throw it into a gratin dish on a foil-lined baking sheet (for easy clean-up) to bake at 400 for 30 minutes. The pasta itself is cooked beforehand with a smashed clove of garlic in the salted water, 2 minutes less than than the package instructions recommend so that it can release some of its starch into the sauce while baking.
Sometimes I'll add a cup of ricotta (if I'm short on milk like last night) & melt that into the bechamel before adding the cheddar, about 2 oz. of freshly grated parmigiano, 2 oz of pecorino and a tablespoon or 2 of creme fraiche. I chop up a few thin slices of prosciutto into thin dice & mix it into the dish before baking it. When I go crazy, I add a Tbs. white truffle oil to the dish & stir it in just before baking.
I'm always conflicted about breadcrumbs but the hubby likes them so I do add a light sprinking of panko (or even Progresso breadcrumbs) with dollops of butter & a grinding of seasonings over the top of the dish after first grating an extra layer of cheddar over the casserole. If the breadcrumbs aren't as crisp after 30 minutes of baking as I'd like, I stick the dish under the broiler for a minute or so until they look good to me.
I made this last night (yummy!) & posting it here so I can remember what I did since it was impromptu & I was low on milk. Hope I didn't take up to much space :>)

I start with a bechemel base. Then add Velveeta, Aged Gouda, and Pecorino. Mmmm...

I will eat any mac & cheese, and have made it tons of different ways, but I made it with a rather odd combination once, Brie and Cheddar, cause that's what I had in the fridge, and it came out surprisingly well. Everyone wanted to know my recipe. Sadly, I didn't not write the proportions down.

I know I'm late to chime in, but I just gotta say:
There's a great substitute for Velveeta which my wife calls "Chernoble cheese".
Merkt's port wine cheddar.

best home made:
Light Cream, ( not Heavy, not Medium, not Half & Half )
while heating, whipping in coarsly grated 5 year old imported Holland Gouda ( $ 7.95 at Sams ), a bit of white Pepper, no salt needed, bits of sauteed Prosciutto, and then the al Dente cooked Ziti, all in buttered casserole topped with grated Tete de Moine 450F oven til brown

My MIL's mac and cheese - no bechamel saucing required (she can't cook otherwise, but this is to die for):

1. Butter a casserole dish (I use a square 2-quart Corningware dish)
2. Boil 2 cups macaroni (I like Barilla elbows because they have ridges)
3. Drain, do not rinse
4. Layer half the macaroni in the casserole, sprinkle with 1 cup shredded cheese. (I usually end up using Kraft or Kroger pre-shredded cheese but obviously it's better with better cheese. Sharp cheddar is my personal choice.)
5. Repeat layers.
6. Mix together (a 2-cup Pyrex measuring cup works well) 1 cup milk and 2 eggs. (My MIL's original directions also say that you can use evaporated milk to make it even richer, but I think that's sort of overkill. My husband tried to use Redi-Whip once...the results are better not described.)
7. Pour egg mixture over macaroni and cheese layers in casserole.
8. Sprinkle a little more cheese over the top. (I've never tried it with crumbs.)
9. Bake UNCOVERED at 325 for about 20 minutes.
10. Let stand for 5-10 minutes to set before serving.

Serves 4-6 as a main dish, maybe more as a side dish, but probably not more than 8 as written. If there's any left, it's as good if not better reheated in the microwave. Also very forgiving of the addition of diced ham, sliced hotdogs, vegetables, etc. Quick and so easy I have it memorized...great for busy weeknights.

I'm in the predominately cheddar group w/ the rest being whatever I have on hand,including cream cheese. I'm in the bacon camp and I also like diced onion or jalepeno,cherry or grape tomatoes.The topping?I've hit on the devilish combo of 1/2 breadcumbs,1/2 CHEEZ-ITS ground up together in the food proceesor.And yes they're buttered.I dont make this too often since it can kill you.