Compare my iTunes library with the iTunes Store's
I looked around and honestly I didn't find a great method to do this, just a plethora of different items. 
If you activate your iTunes sidebar, you can actually go to the album in the iTunes store directly when you are playing or selecting that song.

You can also use things like iTunes preview to compare against your iTunes library, for instance The Beatles page has their songs and albums (though they are called top songs and albums) and you can click on any of them to get a track list.

I found I could copy and paste the track list to a spreadsheet application like numbers while preserving the formatting, and could do the same with an iTunes library exported track list (as text), I then sorted by columns and saw the ones I did have against the ones in the albums on iTunes next to each other.

This isn't a great approach, but it seems like it will take significantly less time than manually printing out song lists and the like, sorry I couldn't be of more help.