Why not make a mod of Aliens versus Predator? There ain´t many ships there (Nostromo, Betty, Sulaco, UD-4L Dropship, Auriga plus the Predator ships and some human ships from the games) but look at the bright side – we can use our imagination to create new ones:). The Predator ships look very cool, IMO. We may also put in the Space Jokcey´s ships. I found some 3D models from the movies, too bad they are for 3DSMax and obviously have too many polys:
http://members.ozemail.com.au/~dproc/
More information about Predator ships:
http://geocities.com/gunsandgod/ship1.html
and more:
http://geocities.com/gunsandgod/ship2.html
Some more information about the ships and other things in the Alien movies:
http://www.planetavp.com/al/index2.htm
Never-EVER forget your real life, though.