"Alien Quadrilogy" that is limited to 200,000 copies worldwide
- Comes in a special DigiPack with 9 DVD's
"The Hulk: Collector's Edition" that is limited to 5,000 copies worldwide
- Comes in a special case, with a reissue of the 1st comic of The Hulk, and 5 storyboards from 5 different artists, etc
These two are "really" limited.
Others that a have, have a "collector's edition" with limited packaging for example, like:
The Fifth Element
Saving Private Ryan
and so one, and so one.
And yes some "Collector's series" are just a marketing trick to attract people to buy the same product...