How do I remove duplicate songs from my iTunes library?
Is there an easier way than just ⌘ Command + Click every other song in the list?
Apple doesn't have anything natively to select duplicate files so, unfortunately, you'll have to resort to a paid solution like Dupin or you could try Randy's Träume's script.
I haven't used either so I can't vouch for how well they work, but forums I found relating to this problem point to Dupin frequently so that might be your best bet if you don't mind spending a little coin.
iTunes does have a way to show duplicate songs, in your library and in playlists.
File > Display Duplicates
Remember that the playlist has to contain more than one track/video/podcast for the "Display Duplicates" option to show.
I am very happy with Corral iTunes Dupes script, which I downloaded from Doug’s Scripts years ago. It seems to be gone now, but I found a modification here.
However, it’s a PPC app (pretty old!), which you have to convert to Intel architecture by dragging it to AppleScript Editor.app
and saving it as Application. You only have to do this once.
Dupin is worth paying for if you are not comfortable working with AppleScripts (which are straightforward in any event)