You liked 5cm animation? You will love Kotonoha no Niwa (Garden of Words) ;)
Together with brilliant voice acting by Kana Hanazawa, it's by far the biggest Shinkai's masterpiece ;)
I also liked The Place Promised in our Early Days, Voices of a Distant Star and Children Who Chase Lost Voices.
I've seen almost anything Shinkai made so it's hard to choose =D