If you haven't already, I suggest checking out Tale of Two Wastelands if you own Fallout 3. It puts the entirety of Fallout 3 into New Vegas' engine, and lets you play it all with one character. The game feels incomplete without it IMO. It's made by some really skilled modders and is pretty stable despite being in alpha.
I will probably never get tired of fnv because of the insane modding scene. Hell, it's even fun poking around, tweaking, and making mods myself.