As far as Megaton Reputation goes, we have the leo stahl thing, the pipes, the survival guide, the bomb, and...I can't think of any others off the top of my head. But in the repairing pipes, you get to sell scrap metal to walter, and he doesn't just put this in a damn cabinet for anything. He repairs the water system of the town with it. Each of these should improve the player's reputation with it. These could incur the gift scripts, discounts in the Brass Lantern Moriarty's, Moira's, and just let you feel accepted with the high karma dialogue.
There is something similiar to be said for Paradise Falls, wherein bringing in slaves gains reputation. Fixing Pronto's supply also gains reputation, however the Strictly Business challenge garners enough reputation gain in the town to get you to liked. And perhaps these increases in reputation equate to access to a higher tier of gift/tribute? liked reputation giving you access to the regular level, but Idolized gives you much higher quality loot/food/water/medical supplies.
Underworld could work similarly with Winthrop's Scrap deal, but a large amount of infamy would be gained by hiring Charon. You killed the vibe by killing the dealer for people. regardless of whether it was the right thing or not, the people in the bar react negatively.
Can reputation be gained in thresholds depending on how much caps are traded in transactions? I work my ass off to keep moira and Doc Church rolling in food, ammo, weapons, and perhaps a trust can be seen in this?