There are differences between the 2003 DVD and 2010 Blu-ray versions of ALIEN: The Director’s Cut:
As the sun rises over LV-426, three helmet lights (representing the astronauts) have now been added, as they make their way round a large rock formation (for the 2010 Blu-ray).
The CGI mist that drifts past the derelict entrance as the three astronauts enter, is now missing from the 2010 Blu-ray.
Alternate take used for the insert shot of the Alien, just before Brett is attacked (for the 2010 Blu-ray).
Not sure about this last one, but the radio static (added for the 2003 DC) heard as Ripley uses the wall com to contact Parker or Lambert - after a confrontation with Ash - may or may not be missing from the 2010 Blu-ray?