We have a complicated way of finding currently available drives on Mac OS X (see LIB-28) and proposed ways for Windows (LIB-43).
The difficult part there is, that device names can also be used as disc drives so we have to distinguish these.

For Linux and the BSDs there are already default device names by convention.
The defaults we currently use mostly work, but could be improved. Especially Debian/ubuntu don't create /dev/cdrom automatically anymore but /dev/cdrom1.
For Solaris we have /vol/dev/aliases/cdrom0, but I also found /volumes/dev/aliases/cdrom0.
For NetBSD /dev/rcd0d is supposed to only be available for x86 installations, but this isn't sure.

It should be easy to do a quick check which devices actually exist (try open for reading) to find out which of these 2-3 options actually works.

For Linux we possibly could do what picard is doing with /proc/sys/dev/cdrom/info if /dev/cdrom* doesn't yield results.