I recently watched "Predator" on bluray and I think I'm convinced more than ever now that the final confrontation/duel between Arnold and the Predator is the greatest human vs alien duel I've ever seen. What are some other good examples?

Some others that came to my mind,

Ripley vs. queen alien in Aliens
Danny Glover vs Predator
Kirk vs. Gorn
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Six months ago hardly anyone knew my name. Now everyone wants to be my friend. I wanted respect. Instead I have become a wishing well with legs. - Londo Mollari