BurnBit has a handy service that allows you to generate torrents for any directly accessible HTTP link.
They have some nice instructions to integrate it into your site. However, almost no big sites use these.
In order to easily use it for downloading Linux distributions (which are well mirrored, making BurnBit useful, even if just easily download from multiple mirrors simultaneously and to check that the file is not corrupted) I wrote a small GreaseMonkey script that injects their download buttons in some of the more obvious mirror sites / HTTP accessible FTP sites.
It is somewhat crude currently, but works well on sites that just contain directory listing.