On Crunchyroll, the Flash streams are all soft-subbed (well, nearly all of them, some series are hard-subbed) and relies on the Flash renderer to display them. Crunchyroll actually sometimes streams subtitles (depending on licensing) for multiple languages.
You just need to right click on the Flash frame (where the video is being displayed) and you should see a list of subtitle options, including at the top "No Subtitles".
Note that Crunchyroll also does HTML5 video, so browser's like Chrome which supports AVC streams through HTML5 will not use Flash. These types of streams are still soft-subbed but the local renderer of the subtitles isn't Flash, and it's probably some plugin-type video player that does this, so how you turn off subtitles depends on your OS and how you've setup the browser.
I couldn't make a screenshot of the Flash menu but this thread on Crunchyroll's forum has one: