MirrorX
You can buy a 320 gig external hard disk, with a USB-capable enclosure, for around $120. That fits all my videos, music and photos, so using one as my backup medium makes sense. It's a lot faster than backing up to a stack of DVDs, and frankly I trust it more.
I couldn't find a tool that would let me easily update my removable drive to reflect changes I'd made to my real photos, images or videos directories, so after looking at quite a few options (xcopy, xxcopy, Unison, rsync), I wrote MirrorX.
MirrorX doesn't try to do a lot; it does one thing, but I think it does it pretty well. It's a command line tool that, given a source and destination directory, makes whatever changes are required to the destination (deleting files or folders, copying files or folders) to bring it in sync with the source.
I created a page for it, with a link to the Google Project page for it, here.