Book: The Never-Ending Story by Michael Ende. Naturally, the original edition with the red and green letters and the illuminations at the start of each chapter.

I had this edition as a child and I really regret that it was given away or donated in some long-ago clear out.

My nomination for 'media that has aged well' is Deep Space Nine. The ongoing plot arcs were ahead of their time and the characters and themes still hold up to a present-day viewer.