You could try Deadlands: Lost Colony, the "Way Out West". It's futuristic with a spaghetti western feel. Also, a fair bit of horror that can be mixed in. You could go with its sister setting, Hell on Earth (post apocalyptic) the "Wasted West". There are d20 rules for Lost Colony, but I find the classic rules provide a much better flavor; if your into that kind of thing.
Also, Shadowrun is a good game for a futuristic vibe, I mean, it is set in the future. D20 Modern I'm not sure on, but it's close. Oh, the Savage Worlds system has at least two settings that might work. One specifically is Slipstream. Think Flash Gordon instead of Star Wars.
That said, Prime is absolutely right. You can paint any system with a coat of future. Just gotta get the mix right. Good luck!