Seeing the thread in the Tron forum got me thinking about The Two Towers, where I recall a lot of missed chances for riffs.
For instance, off of the top of my head, when Frodo says "You've left out one of the chief characters" at the end, it would have been the perfect chance for someone to say "Glorfindel." Or "Radagast." Or "Bill Ferny." Or even "Tom Bombadil." Or any character who got cut from the book, really. Instead, no line at all.