Here's a list of instances whose classic form has been altered/removed sometime in WoW:
-Naxx40
-Zul'Gurub 25
-Scholomance
-Scarlet Monestary (all of it)
-Sunken Temple
-Shadowfang Keep
I feel like these should be reimplemented, in some form. I'm not saying get rid of the current ones, but add a 'classic mode' option to the dungeon difficulty screen that would allow us to see the Pre-Cata version of all these instances. A lot of people I'm sure would like to see the old content and get a shot at the items/gear pieces/profession patterns that these old raids/dungeons had. I don't think any of these should have been removed in the first place.
Anyone else want these to be reimplemented?