This seems to have fixed the issue: on your desktop, hold down the [OPT] key and click on "Go" in the menu bar; holding down the [OPT] click on Library, find Preferences, and then delete all the files that start with "com.apple.itunes.XXXX.plist" where the "XXX" is whatever other things may exist - as long as they end in "plist". From my experience, preference files are rebuilt by the system after the next restart, so you have very little worry of losing any important data; the worst that could happen )and NOT in this instance, but for other plist files) is that you may have to reset the application "preferences" again when you next start it up, to act or appear in a "preferred" customized way for you.
Once you delete the .plist files, empty the Trash, and either log out or restart the computer. Once you're back up and operational, start iTunes and your iDevices should reappear in the sidebar (if that's open) and/or at the top of the screen (if that view is enabled).
Hope that helps. It definitely fixed my problem!