some random ideas........
shopkeeper: competitors cheating, nagging wife, bar wenches, local economy is crappy or going really well (this could tie in with the supposed ability to affect things in the game world), new shipment coming in, taxes, local politics, etc.
random knuckledragger you meet on the street: mudcrabs, bar wenches, weather, recently spotted dragons (could be used by the player to maybe help find them, obviously check more than one NPC since rumors are often false), nagging wife, suspicious neighbor, someone hasnt been seen for awhile (presumably you killed them at some point but nooone saw you), suggestions for best eating or equipment establishment (they could notice that you wear heavy armor and use axes and direct you do the store that is currently selling them the cheapest), local politics, etc.
fighters guild: football, cars, chicks, music, lots or references to "playing swords" with their fellow guild members, burping contests and arm wrestling (both of these could be interactive possibly quick time events), there last kill etc.
mages guild members: calculus, chess, video games, star trek specifically who is the greatest captain, WoW, what they should do if they actually meet a chick and she shows any form of interest, they also like to "play swords" with each other........weird cause dont they usually carry maces?
dark brotherhood: latest poison that backfired on them, how they almost got caught or how they got clean away, the boss is not happy with them for some reason (after this conversation occurs you dont see them again ever) the proper way to use shadows to hide yourself and how invisie and chameleon spells are for losers who svck at games, assassins dont play swords......they play daggers, the local politician they just killed, etc.
just some basic ideas.....obviously some of them like football wouldnt work cause its an earth game but you get the general idea.