In addition to ger-el’s message, there are may other versions of the unaltered movies (16mm preservation by Puggo Grande, LaserDisc preservations, VHS preservations…), which have a true historical interest and are very enjoyable, but are less “comfortable” to watch if you just want to have a theatrical-like experience.

IMHO, if you just want to enjoy the unaltered movies with good image and sound, the best choices are :

ANH: Harmy’s Despecialized Edition 2.7 (more “Blu-Ray like” with sharp and clean image) or Team Negative 1 35mm scan 1.6 (more “theatrical experience” with grain)
ESB: Harmy’s DE 2.0 (more “Blu-Ray like” with sharp and clean image) or Team Negative 1 Dreamastered v2 (more “theatrical experience” with grain)
ROTJ: Harmy’s DE 2.5 (it is the only choice, because the Grindhouse version is not yet cleaned/regraded)

You can find all versions on MySpleen, Usenet or some public torrents.