This is pretty obvious, but the leader of the orcs in the Battle of the Pellenor Fields (Gothmog?) has a startling resemblance to Sloth from The Goonies. When I was watching it for the first time I actually yelled out "HEEEY YOOOU GUUUYS!"
Now that I think about it Sean Astin was the main character of The Goonies! Maybe he got the creature creator to do him a favor and get his misfigured friend a cameo
