In Safari, when you type in natural text or something similar to the title or URL of a site, Siri suggests a site. I must say, it is really good! I'm not sure if Apple has restrictions regarding Siri in 3rd-party apps, but having this would be really cool and would enhance the search experience greatly.
Here's what it looks like in Safari:
When someone searches something with natural text or mistypes a url, a Siri suggestion should pop up at the top.