I've been looking around the wiki to find other lost media and on the web. I came across a few animated movies that are considered to be lost, yet they don't have their own articles.
The Adventures of Pinocchio (1936 film) - This was suppose to be the world's real 1st animated feature film as well as Italy first animated feature. The movie was later canceled for unknown reasons.
Various Asterix Movies - This franchise has quite a number of feature films that are lost or never completed.
Here's a website containing information about these lost films - https://web.archive.org/web/20081218204515/http://www.asterix.co.nz/movies/lostasterixfilms/index.html - Note: This website is no longer online but you can access it via "The Wayback Machine".
Original Version of "The Thief and the Cobbler" - I'm aware of the Recobbled Cut, but from what I know it's still missing quite a bit of scenes from the original production between 1964-1990 (under Richard Williams control).
I would create these articles myself but I am still a bit nervous to do so (due to being completely new to the whole Wikia world).