I have a WD MyPassport 1TB portable drive model WDBABM0010BBK-00. Been working great for about a year or so, maybe a bit less.
Today, all of the sudden, it stopped showing up when plugged into my laptop - Mac OS X Mountain Lion 10.8.2. Tried it on 2 separate laptops, same story. The LED light does go on when plugged in.
It doesn’t show up in the Finder, nor in /Volumes, nor even in Disk Utility. Hundreds of GB of data on there. Most is backed up, not all.