NOB would be cool. I was thinking it would be cool to have a uranium enrichment plant.
That way I could fly the in game Apache and blow it up.
A NORAD might be cool too.
Talltower - if you are really looking for ideas, i really would like to see smaller medium density housing(2-8 stories) with ground floor retail.
Also some larger high density buildings with built in subway stations.
3.2 words : Walled City of Kowloon
Batcave