Whether connected to a Mac or a Windows PC, your external drives can accumulate junk files created by the operating system. CleanMyDrive is an app that targets those files automatically and wipes them out to help you avoid wasting any space. It also makes it easy to eject any external drive, or all of them at once, with a single click.
CleanMyDrive lives up in the menubar and can work automatically or manually -- it's your choice. It's almost unfortunate that the interface is so nice because you will rarely need to interact with it. For the most part you can just let it run in the background and keep your drives from accumulating junk files. If you need to eject a bunch of drives, however, it's conveniently available.
It can even eject them all at once with a single click, or just eject all disk images you've mounted. This is a nice little upgrade to OS X's eject menu. CleanMyDrive is a free download on the Mac App Store, so give it a try.
CleanMyDrive (Free) [Mac App Store]