Buying it Tuesday! I can\'t wait! So many changes! Lets get some SERIOUS updates to this thread...
First off, a quality of transfer update. The best quality home release to date has been the Laserdisc editions from 1995 which were, I believe, the original versions of the trilogy. Here are some comparison pictures compliments of Manabyte on the GAF boards.
1995 Laserdisc:

2004 DVD:

1995 Laserdisc:

2004 DVD:

Now, that\'s pretty impressive. However, here\'s some stuff that may turn off many hardcore Star Wars fans compliments of ign.dvd. Here are some shots of the changes to the DVD editions of the films:

The revamped Jabba the Hutt. You can see the original in this thread to compare.

No comment on this one. I can explain WHY he\'s there for those who don\'t yet know, but it does tread into spoilers for Episode III so It\'s really on a request basis only.

The much improved lightsabres.
Now, here\'s some things that are not (and are) pictured that are changes to the dvd\'s. It\'s just a list so enjoy them for what it\'s worth...
Episode IV: A New Hope
# Lots of matte lines removed. The space under Luke\'s speeder looks much more realistic.
# R2D2\'s blue parts are much cleaner and more consistent.
# The 1997 animation added to the entrance to Mos Eisley is much smoother.
# Greedo and Han shoot at the same time, and Han\'s dodge is far more realistic.
# Jabba has been retexturized and looks considerably better. Han still walks on his tail, but it\'s much smoother.
# The lettering on various Death Star panels are written in Aurebesh rather than English.
# The matte-painted hall in Leia\'s detention block looks much more realistic.
# Lightsabers look much better. Colors are far brighter and the blades are more defined.
Episode V: The Empire Strikes Back
# Ian McDiarmid has refilmed scenes as the Emperor instead of that near-fossil they had.
# The conversations between Vader and Palpatine has a few new lines. Palpatine knows that Luke is Vader\'s son.
# Light sabers are again fixed, making them more consistent.
# Temuera Morrison does the voice of Boba Fett
# Luke\'s inane scream when he jumps to escape Vader on Cloud City is gone. And there was much rejoicing.
Episode VI: Return of the Jedi
# Like the other two, the light sabers are fixed.
# The Rancor looks considerably better, with its matte lines removed.
# When Vader\'s helmet is removed, his eyebrows are gone and his eyes are recolored to match Hayden\'s.
# Celebrations on Naboo, Coruscant and one other planet, where a statue is toppled right before we see the celebration with the ewoks.
# Perhaps this was in the 1997 special editions, but in the various background shots of the new Death Star, its appearance changes and you can see progress as the station takes shape.
# Hayden Christensen replaces Sebastian Shaw as Anakin\'s ghost. Lucas explains this in the commentary, which is spoilerish for Episode III.
Anyways, I\'m excited. I can\'t wait till Tuesday!