Hm, only some heuristics - very fragile, but maybe they work for you:

Output of mount: a mounted CD/DVD has usually a filetype of iso9660 or udf and an ro attribute. USB sticks, -drives, iPods, etc. are often mounted with the flush attribute and might have filetype vfat (not sure: ntfs, msdos).

pb> mount | perl -ne '@mnt = split /\s+/; print "Stick? $mnt[0] $mnt[2
+]\n" if $mnt[4] =~ /vfat|msdos|ntfs/ && $mnt[5] =~ /flush/;'
Stick? /dev/sdd1 /media/BLUESTICK
Stick? /dev/sde /media/IPOD

pb> mount | perl -ne '@mnt = split /\s+/; print "CD/DVD? $mnt[0] $mnt[
+2]\n" if $mnt[4] =~ /udf|iso\d+/ && $mnt[5] =~ /ro/;'
CD/DVD? /dev/sr0 /media/SOYLENT_GREEN
CD/DVD? /dev/sr1 /media/IX0712
[download]

.oO(mmmmmhhh Soylent Green™...)

lsusb -v lists the USB devices currently attached but not necessarily mounted. Check e.g. for attribute bInterfaceClass 8 Mass Storage. Though, you might find empty memory card readers, iPODs, everything that has a filesystem interface...

pb> lsusb -v 2>/dev/null | \
    perl -ne '$dev=$_ if /^Bus/; print $dev if /bInterfaceClass\s+8\D/
+'
Bus 002 Device 006: ID 05ac:1301 Apple Computer, Inc.
Bus 002 Device 006: ID 05ac:1301 Apple Computer, Inc.
Bus 002 Device 005: ID 1307:0163
Bus 002 Device 004: ID 05e3:070e Genesys Logic, Inc.
[download]

Use with care.