There are tons of original ALIENS art pieces posted over at comicartfans.com:
http://comicartfans.com/SearchResult.asp
Type in ALIENS or Predator to see the original art pieces and click the thumbnails for bigger high rez pics of the art. There are a bunch of pretty cool old comic pages in b&w too. Some nice covers too without the original comic logos and titles.
There're even Star Trek/Aliens comic art pages in there. Was that a once planned/proposed series???