To get authentic "movie theater" popcorn, don't forget the seasoning! Popcorn salt is a MUST if you want to replicate the taste you get in the theater...although, I must say, REAL butter tastes SOOOO much better than the butter flavored oil they use in theaters now!
Also, get CREATIVE! I like to use garlic salt and paprika on my corn...experiment a little with the spices in your kitchen!