I believe it was Kiki's Delivery Service.
I think I saw it at my grandmother's house at one point, and from there I simply got curious about what other stuff this studio had made!

Pom Poko is still my absolute favorite of them all, though.
It's utterly underrated, it's a lovely and fairly bittersweet story of nature and humans and mythology. I can sort of see why it's not as popular in the West, because the Japanese raccoon dog doesn't have nearly the same significance in folklore outside of Japan, but.. it's still worth a look.