Uncover Disk Secrets with Drive Manager
Drive Manager is a nice little utility which becomes more useful the more drives--including USB keys and the like--you use regularly. While Windows has some of this functionality built in, it can be a pain to access (you have to burrow through a good bit of the Control Panel to find it), and it doesn't include the level of detail you get through the free/donationware Drive Manager.
Drive Manager shows all active drives in an easy-to-read display, though you can toggle some things (such as CD or unmounted drives) on and off as needed. You can map a folder to a "Substitute" drive, for example making your Documents folder into your "D" drive, which can be useful for file sharing purposes. The disk information screen is exhaustive, showing a plethora of disk properties, right down to the serial number (possibly useful for hardware inventory control).
However, Drive Manager is not without its flaws. The program is marred by typing and spelling errors in labels, and I experienced several bugs in general use--none fatal, but they were annoying. Since Drive Manager is free, I would recommend downloading it and seeing if it is useful to you. It is the subject of active and ongoing development, so we can hope that the issues I encountered will be cleared up soon.