Like any good tool, Rsync can be easily used to destroy your life. In my case it was a typo on the destination directory and use of the "--delete" option. Just like that, my SD card was emptied. Luckily I didn't have too many files on there, as I only recently acquired it, but there I was thinking "boy I wish I had backups of that". The good news is, I found PhotoRec.
Don't let the name mislead you; PhotoRec is capable of scanning a number of modern filesystems and look for signatures of common file types such as images, music, and documents. It doesn't require an intact filesystem but it certainly helps. I won't go through the ins and outs of the process as the documentation does the job quite nicely.
Photorec can't do everything, of course. It did find what appears to be all of my files, but the names are left up to me. That's a problem I can live with. Having more than once scanned through a dd image of a disk to scrape out data, I have been thoroughly impressed.