I have another one:
$ for F in /dev/s* ; do echo "$F $(cygpath -w $F)" ; done
/dev/sda \\.\PhysicalDrive0
/dev/sda1 \\.\STORAGE#Volume#{781f8bd6-7d0d-11de-8012-806e6f6e6963}#0000000000100000#{53f5630d-b6bf-11d0-94f2-00a0c91efb8b}
/dev/sda2 \\.\Volume{781f8bda-7d0d-11de-8012-806e6f6e6963}
/dev/sda3 \\.\D:
but there are two problems.
Up to the current Cygwin 1.7.6 the info from /proc/partitions is
incomplete for non-privileged users. I just checked in a patch to
Cygwin which allows the full partition info also for non-priv'ed users.
Apart from that, the output of cygpath -w for devices isn't overly
helpful yet. I look into improving that a bit.
Corinna