Ken pointed me to a great link with visual and audio comparisons of changes to the Star Wars Trilogy. From the standard Widescreen VHS versions to the Special Editions and recent DVD releases, the list is pretty comprehensive. What DVDAnswers did miss, readers note other changes in the comments sections.
I tend to agree with most of the comparison thoughts, although I do think the new Jabba in the DVD version of A New Hope is closer to the Jabba in the Return Of The Jedi. The Hutt may appear more plastic-like, but his overall look, as evidenced by his facial features and body shape, is closer - even if he is a bit younger.
The site is also experiencing heavy traffic and there's a lot of images, so be patient.
Star Wars: The Changes - Part One - A New Hope
Star Wars: The Changes - Part Two - The Empire Strikes Back
Star Wars: The Changes - Part Three - Return Of The Jedi