How to clean up duplicates in iTunes library?

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.