Mount your USB drive so it appears as /media/music every time. Mount your FireWire drive so it appears as /media/data every time.
My storage setup on my Ubuntu box at home is a bit unusual. I have an external drive dedicated to music and another external drive that backs up the music drive. I also have an external drive to hold all my personal documents, pictures, and movies, with another external drive to back up that drive. Those four drives are all connected to my desktop via FireWire. Finally, I have an external drive that's a temp drive: when I download a new movie or set of pictures, or rip a new CD, I keep those files on the temp drive until I can properly place them on the music or personal data drive. Unlike the other four, the temp drive uses USB.
Five drives sounds cool, but there's a major annoyance associated with them. When I reboot Ubuntu (a rare occasion, to be sure, but it does happen), their mount points shift around. Sometimes FireWire drive number one gets /media/sdb1, and sometimes /media/sdc1. The same thing happens to the other drives as well, which wreaks havoc with my backup scripts and my attempts to SSH in from other machines, to name just two problems I've experienced. I want persistent naming of those drives, so that FireWire number one is always /media/<something>, FireWire number two is always /media/<somethingelse>, and so on.
After much searching, I found the answer on the Ubuntu forums, at http://ubuntuforums.org/showthread.php?t=91948 ...