I want to see how my local working copy differs from what's on the server.

Can I do that without downloading the entire site to my local machine?
Is there a "diff" tool that diffs betwixt files here and there?

I imagine the challenge there is that something will be reading every file via FTP, and in my case that's going to take a long, long time.

On the other hand...
A line-by-line analysis isn't necessary. I really just want to see which files exist on the live site that aren't supposed to be there. Because when I "publish" stuff, it pushes files over to the sever, but it doesn't delete things that I delete locally. That leaves behind a lot of orphaned cruft.