I like to be able to easily see and access mounted volumes on Mac OS X, without having to go to the Finder, so I use this simple trick to add a list of volumes directly in the Dock, just like the “Downloads” folder.

In the Finder:

Click “Go” in the menu bar and type /Volumes in the dialog box.  This will select the Volumes directory (which is normally hidden).  Simply drag this to the folders area of the Dock (next to “Downloads”).

For Terminal Users:
Open Terminal.app and type the following command:

open /Volumes

Hit return, and Finder will open at the Volumes directory.  Simply drag this folder to the dock for easy access.