Look in /Library/Caches/Safari.
However, be forewarned: they're all .cache files. While these do store the data in a recognizable format, that's not all they store. They also have data on what appears to be how the browser was configured when you opened the page. As a result, .cache files do not open "as is" in the usual viewer for that particular type of file; you will have to scrape the data out yourself.
Plus, the filenames are in the form of reallylongnumber-otherreallylongnumber.cache, and they're in a folder structure that nobody seems to understand at this point. So getting things like QuickTime movies out of the cache is going to be an adventure, to say the least.