I've been totally remiss in not blogging about Xenomurphy's wonderful Arkham. This thing is gorgeous, completely full of details. You've got to download the book he put together showing it in all its glory.
OliveSeon is, I believe, a professional builder in Korea, who puts together very large and detailed displays. This movie studio theme park includes a huge rendition of Stark Tower and the wormhole opening up for the Chitauri fleet.
Jbuttles has made a great rendition of Gotham City police headquarters, completely furnished with details like a crime lab and Commissioner Gordon on the roof with the Batsignal (hmm, sounds like a game of Clue).
Check out this great Batcave by Jbuttles. I love all the details, like the memorial to Jason Todd's Robin costume, the hidden exit for the Batmobile, and the trophy display (especially the famous giant penny).