A Disney movie was almost certainly my first. Looking at re-release dates on IMDB, I'd say Cinderella is the most likely candidate in 1987 or more likely early 1988. I was 4 or 5 years old (depending on when we went), and I do remember seeing it at the Villiage 8 Theaters here in Louisville. Lady and the Tramp is also possible, but that was re-released a year earlier, and I'm not 100% sure that I saw it in the theater.

The first live action movie I remember seeing in theaters (also at Villiage 8) was National Lampoon's Christmas Vacation in 1989.

-Eric