Anyone have any lists of good quest mods? I'm looking for ones that would be fun and challenging to higher level characters. Also, ones that have a Fallout feel (like they feel like they are part of the game) and preferably they don't directly effect the main game (have no effect on the main plot or story or change any of the original characters).

Well, I will plug my own quest mod, at http://www.gamesas.com/index.php?/topic/1160937-rel-decisions-with-regrets. Join a medical research project which may help a problem sweeping the wasteland ... but is the cure worse than the disease? Decisions with Regrets is a medium size quest mod, with emphasis on conversation and moral decisions rather than combat.

I'd highly recommend Tales of the Burning Sands Part 1: The Chef. I just played through it and it's incredibly well done. Definitely has the Fallout feel to it too. You can find it on New Vegas Nexus. Also, New Vegas Bounties is another one you should check out, it's got some good high level fights in it.

A World of Pain is great if you like the challenge of combat. No storyline, though, just great new locations with baddies.