Most of the time, I go for the classic: melted butter and salt. Actually, to be fair, most of the time I go for whatever they serve at the movies, which is certainly not butter. Occasionally, I also indulge in an overpriced box of Milk Duds, and pop one of those in my mouth along with as much popcorn as I can stuff in without choking. Makes for a great bite by bite do-it-yourself popcorn ball experience.
A distant overall second has to be microwave popcorn, but I don’t tend to customize (or enjoy) it at all. Sad, really…
However, when I go all out and pop my own, fresh popcorn from scratch on the stove in a big pot with corn oil…that’s when I indulge in my all-time favorite: real butter, salt, and nutritional yeast flakes. Just enough to put a light coating on all of the butter-covered pieces. Mmmmmmmm!!!
So what is your peculiar popcorn passion?
A couple of foodies on another forum have been experimenting with using truffle salt on their popcorn.
I like Orville Redenbacher’s pour-on cheddar butter.
In a more gourmet mood, I use fresh-grated Parmesan.
Mrs. Furthur
For other curious folks: http://www.bookofjoe.com/2005/06/truffle_salt.html
I’ve never had truffle in any form, so I’m at a loss to imagine what this would taste like, but you never know when opportunity might strike.
No way is there 40 grams of truffle in one jar. One jar is only 100 grams and, just by appearance, it looks to be about 10% truffle. Either way, it’s a marginally economical way to appreciate the full wonder of truffles. You only need about 2 or 3 grams of truffle salt on popcorn to get that oomph, that works out to be less than $1.
I must admit an alarming weakness for Pop Secret Homestyle microwave popcorn. It’s the only kind I can eat an entire bag of without a second thought! It always surprises me how much I love that popcorn, because typically I don’t like the taste of that much salt.
When I’m not being so lazy, I pop my own on the stovetop with oil. No butter, no salt, just fresh-popped goodness. Yum. 
I don’t care for movie theatre popcorn: the yellow topping doesn’t bother me as much as the saltiness, and I like popcorn that’s fresh and warm (not just top-layer warm from sitting under a heat lamp).
My particular popcorn passion is microwave kettle corn, topped with fresh-grated extra sharp cheddar cheese and then returned to the microwave for 15 seconds to melt. But now I can’t find the snack-size kettle corn anymore, and the regular size is too much for my surgically-altered stomach to handle.