Off the bat in the base game alone we have Cazadors and Nightstalkers, both created by Big MT.
It also appears the spores were started there, leading to both the Vault 22 deaths and some of the deaths Randall Clark saw in the Honest Hearts DLC.
Of course much of what made the Sierra Madre what it has become is Big MT from the cloud, ghost people, even the bomb collars as Elijah took them and the idea from Big MT's unwilling prisoners used as Guinea pigs.
Then of course there is Lonesome Road, as the extreme weather is also thanks to Big MT, and one could argue that if Ulysses didn't meet what remains of the scientists there, let alone Elijah who he pointed towards the Sierra Madre, maybe he wouldn't have been able to activate any of the nukes. (Of course that wouldn't effect too much as our Courier would probably still have unintentionally set off the initial nukes).
What you guys think?