@vpg - Expanse - It's a series, not a standalone film, but its has an amazingly diverse cast with multiple cultures (both derived but current real life cultures and fictional future cultures)

Serenity - Stand alone movie for the series Firefly (you can watch the movie without watching the series)

Event Horizon and Alien (the first one) - Both really great space horror

I'll add Sunshine - I haven't seen this one but its on my list to watch