-The village storyteller: He's the keeper of most of the village lore, and is the person to ask about local legends. He can often be found recounting tales to keep the children entertained, or reciting popular legends on feast-days. Outsiders can, maybe, talk to him about a given legend or bit of local information, but they'll have to be polite, treat him with respect, and maybe buy him his favorite drink, if you meet him at the inn.
-The civic official: He brings news, proclamations, and other bureaucratic stuff from the ruling baron, earl or king to surrounding places. He may have important information for the PCs, or the DM may simply have him saying things to give some extra flavor to the background, and show that other things are going on in the world around them.
-The shifty, quiet characters: They may indeed have secrets they don't want to share, and are wary and nervous. But, as it turns out, their plots are of no threat to the PCs-a merchant on his way home from an economic spying mission, wanting to return to his masters; a courier brining a message between two lovers forcibly separated; a group of merchants trying to find a way to sneak some of their richest goods in without being taxed on them; all of these people have good reasons to keep to themselves, but they do not have any malign intents, and may be completely incidental to the current plot.
-The gossipy servant: Ever wonder what the lord of the manor is up to? Well, his servant has a hollow leg and a loose tongue, and the man is privy to much of the gossip going on among his master's friends, their various indiscretions, and who is being frozen out of the current social scene. He may give the PCs useful information, or he may just be a humorous diversion. He may provide information to would-be social climbers, or he may confirm their suspicions about the debauched upper class.
-The dockworkers and rivermen: These guys are the equivalent of blue-collar freighters, truckers, and construction workers. They may cause fights just for the hell of it, and be the fantasy answer to Archie Bunker, or they may make fast and ready friends who provide all sorts of information, contacts and support for PCs, telling them how and where to hide, doing something like giving PCs a place to hide or free transportation if the PCs do them a favor.
-The circus performers: They're not regulars-they're wandering performers who juggle, sing, tell jokes, do acrobatics, and all the various other things real-life circus performers do, giving the innkeeper a share of their profits before setting out the next day. They may be evil cultists or slavers in disgusise, or they may just be what they seem-wandering performers who make for some interesting role-playing experience, even if you only see them once.
-The street priest: He's the kind of priest you'd see operating soup kitchens and women's shelters, or counselling drug addicts and alcoholics, in real life. Whether or not he has clerical power, he does the same thing his real-life counterparts do: feed the hungry and sick, take care of people, especially women and children, who need a safe place to stay, help pregnant women with their births, help care for drug addicts and alcoholics, and all that.
The priest may be in the inn having a drink to deal with the stress of his occupation, or he may come in every now and again to pay for food for his charges, or seeking them out and try to keep them out of trouble. In any event, lots of interesting adventures can come through a character like this, especially when you consider that he probably doesn't have much in the way of resources to fight back against bullying town guards, street gangs, and anyone else who harasses them. Any coin he does manage to gather he has to spend on food, medicine and other supplies he needs for his humanitarian work.
So the NPC slapped him with a glove and challenged him to a duel. The PC slapped him back with a gauntlet and accepted. 
They traded witty insults the whole time. Much fun was had, and later, the PC decided this was exactly the kind of guy he needed to come along and help with the quest he had taken up. Much more fun was had. 
