I have always loved the title card images as I thought that they were very atmospheric. I even included my scan of the Mysterious Forest title card on the banner! I will talk in-depth about the title cards as a collective some other time, but for now I just wanted to focus on the title card that featured the planet Eternia. Did you know that there were three versions of this one particular title card? The first appeared in "Diamond Ray of Disappearance" and numerous other episodes. The second which first appeared in "A Beastly Sideshow" retained the same image of Eternia, but they altered the position of the stars. This is because Eternia is actually painted on a cel! The third and final image, which appeared in season two's "Day of the Machines", remained until the end and was the same as the original title card. BUT if you compare the first and third images, you will see that the artists created a painted overlay for Eternia; shading the left hand side of the planet, and increasing the red glow to the right.
(click on the images to see them at full-size)