Ejection Seat will allow you to eject a troublesome disk, especially one that the Finder claims is "in use." It will tell you what application is using the disk, and can then force quit and/or force eject the disk. After running this application, the Finder may no longer recognize other disks inserted into the same drive. Force quitting the Finder, logging out and back in, or rebooting the computer should fix this. This application is just meant for quickly removing a disk when you don't want to reboot.