Voices of a distant star, or Hoshi no Koe, is one of my favourite animes of all time. It's only around 25 minutes long and yet, it has won numerous awards. The anime was released around year 2002 but the animation is very good for that time. The scenes are beautifully drawn, one of the best I've seen in an anime.
The entire anime was done by the famous Makoto Shinkai, who is well-known for his artistic skill and creativity. He is also regarded as the new generation of Miyazaki, the man behind movies such as Spirited Away.
The anime uses a good mixture of 2D and 3D art. It's about long distance relationship between 2 high school junior students. The only way for them to keep in touch with each other is through mail messages.
It's a very touching story and a must watch if you're an anime fan.