[flaccideagle]

Also the Hot Wheels 1:18 Batmobile is a good fit.

Chap Mei and Toys R Us's TRUE HEROES line will work as well.

The Narnia castle is one i've been meaning to pick up for a while now.
An example of how it scales with MU:
Marvel News Reviews Images and more - MarvelousNews.com

also note this guy added a ML Doom base to the top of it.

Also, I am pretty sure this is overscale, but a good base for a custom SHIELD whatever.
Amazon.com: Muppets in Space Miss Piggy Swine Trek (Star Trek Spoof) Playset: Toys & Games