Regarding trailers (for Alien, at least), the Quadrilogy has complete sets, but for some reason the trailers that were previously included on the laserdiscs (and the PAL VHS tapes I had!) haven't been duplicated (or even re-linked) in the main trailers section - you have to go into the laserdisc archives for these (such as teaser 2 without the movie footage). They are all fullscreen, so it sounds as if the additional Galaxy and Beyond versions would make an important contribution if some of those are widescreen.
Of course, there are also 30- and 10-second TV versions but these are also included in the Quad.
Ok, I'm going to look through everything that's been mentioned here and try to draw up a contents list for my compilation discs - I will of course only be looking for materials not commonly available, with the possible exception of the Galaxy and Beyond trailers.