Every time I calibrate or change something in my setup I run to SW: Episode I for the 3 way saber duel at the end, for sound I hit up the pod race. Just got the A2 and it has never looked this good. I replaced my older Sony upconverting player with it and am very impressed with it overall, though even the sony did a good job (to my eyes).
So there is a vote for episode I. But if Star and Wars are in the title you know it's going be good upconverted, time was well spent on these releases.
The Indiana Jones trilogy isn't too shabby either.
And oddly, alot of TV on DVD looks really good upconverted. I was very impressed with the Buffy and Angel Boxsets, and Firefly as well (must be a Joss Whedon thing). Twin Peaks looks great. I haven't touched my X-files disks in years, but I was thinking of re-watching some of my favorites from Season 3, we will see how they turn out.
Oh, and on that topic - I sadly didn't get heros on HD since I got a great deal from a local mom and pop on the SD version (sub $30), and it looked great (and that was on the old sony.)