Its hard to say, Theres some fantastic mods coming along.
But the one that has peaked me so far is:
New vegas bounties http://www.newvegasnexus.com/downloads/file.php?id=37310
Its allows you to indulge your inner Bobba Fett.
You dare misspell the name of the great Fett? :stare: It's Boba! One B!
Seriously though, New Vegas Bounties is a fantastic mod, one of the best questmods I've seen actually and I've been using mods since the mod community for Morrowind was just getting off the ground.
If you're looking for a house for your character, then allow me to shamelessly plug two of my own, you can find both in my signature and they both fit into the world. I don't make mansions or top secret millitary bunkers, I make houses that ardinary people struggling to survive in the wastes would build or inhabit, and I've got two for NV so far. One is in the abandoned shack outside Goodsprings, the other is a completely new building in Primm. The latter takes the scavenging theme to an extreme and is filled with all kinds of junk and loot, there's not even a whole bed, just a matress on top of some sheet metal and cinder blocks.
They both come with stoves that work with survival crafting, mirrors that allow you to alter your hair/facial hair and workbenches/reloading benches.
As I said, it really depends on what kind of mod you're looking for.