I just found this website and hope someone can help me recall a movie I have been trying to figure out for about 20 years. I watched this sometime between 1985 and 1990, but it could have been made long before.

The movie was about an alien on board a spaceship killing the crew. The scene I remember the most is near the end only a man and woman are left alive. They manage to trick the monster into an airlock and shoot him into space. Then the final twist is that the girl was just dreaming that they killed the monster and the movie ended with it right behind them.

Thanks in advance.

The way you described it, sounds a lot like 'Alien (1979)', but in the end of that film there was only a woman and a cat alive. She did indeed flush the alien out of the airlock though, however she wasn't dreaming.

Sounds like it could be Creature (1985) - IMDb (http://www.imdb.com/title/tt0088961/?ref_=fn_al_tt_3)

Thanks for the input. It is not Alien but it very well could have came after the success of that movie. Its not creature either. I have asked this question many times elsewhere. Never to any avail. I am starting to think this was just a dream of a nine year old boy that I convinced myself was a movie I saw. I have some other details but I am not sure if I made them up or remember them.

The last surviving man was fat.
They wore yellow jumpsuits.
A man in a top hat did magic tricks and got killed by a tentacle monster.

Its like a cheesy 80s remake of It the terror from outer space

This may be an extremely long shot, but have you tried Star Crystal? The reviews have more information than plot summary does.
Star Crystal Reviews & Ratings - IMDb (http://www.imdb.com/title/tt0092006/reviews?start=10)
Star Crystal - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Star_Crystal)