A long time ago I had a need for downloading a directory listing of mp3 files, there were hundreds. I didn't want to burn the websites bandwidth and was in no big rush to download everything.
This command will download all mp3 files found up to 2 directories deep, it will only download at 120kb/s and it will wait 20 seconds between downloads. no-clobber will ensure that if you need to stop and restart the command, it will skips files already existing. If you stopped the command in the middle of downloading a file, you need to delete the file as it will be incomplete but won't be overwritten when you restart the command (no-clobber is name based, not size).
wget --recursive --level=2 --no-parent --limit-rate=120k --no-clobber --wait=20 http://domain.com/directory-listing/ *.mp3