For air-popped popcorn, instead of salt and tons of butter, I use Mrs. Dash Table Blend and a table spoon or so of heart healthy spread, melted. Put the popcorn in a storage bag, shake in some Mrs. Dash and the "butter" and shake it until it's all blended. Yummy and still healthy!
I have used "I Can't Believe it's Not Butter Light" but other healthy spreads would probably work, or a light buttery spray, too.