The other day I accidentally dragged the icon for my USB memory stick from under the DEVICES heading within Finder. I must have been holding down Command too because the drive icon promptly disappeared in a puff of smoke. I had deleted it. It’s OK, I thought. I’ll just unplug it and then reinsert it. I did so, but it didn’t reappear.
Finder now assumed that I didn’t want to see mentioned ever again the USB memory stick. Brilliant. I had no way of ejecting it short of starting-up Disk Utility (in the Utilities folder within Applications).
The solution was to insert the stick, open Finder, hit Shift+Command+G, and in the dialog box that appears type /Volumes. Here you’ll see any all storage devices attached to your computer. You can right-click them to eject them, but to return a missing entry to beneath the DEVICES heading of Finder, just click and drag it there.