The movie "Molli and Max in the Future" was pretty fun; a gonzo sci-fi version of When Harry Met Sally.
I'm trying to think of other sci-fi movies like that... Hitchhiker's Guide to the Galaxy of course (though I've never really enjoyed the adaptations). Fifth Element, Galaxy Quest, Barbarella, Buckaroo Bonzai...
There's some more dystopian ones like Brazil, Moon, Zardoz...