In Vegas? No, but there's a quarry full of deathclaws if you feel like a challenge.
There are no Behemoths in New Vegas, but I'm sure there are legendary monsters who are strong as those.
I haven't played New Vegas yet, but from what I have read about it, no there isn't. The Super Mutants from New Vegas are Mariposa Muties, only Vault 87 Muties turn into Behemoths.