Renting out a room to a stranger

It would most likely be a Realtor here. I don't know how often they're used for just apartments, though. The only times I've dealt with agencies when looking for apartments was when I was trying to find an apartment to rent and they owned a bunch of buildings (in which case they were more of a landlord than anything else). George's first job in Seinfeld was actually as a realtor for rental properties in NYC, actually.

I'd recommend advertising at work/school first, and if that doesn't work out you can try Craigslist or the newspaper. You have to remember that you own the property here, so you get to make the rules and you're responsible for having things working.

You'd need to set up guidelines for guests (overnight and otherwise), utilities (including cable and internet, if you're going to have them), sharing of pots/pans/dishes in the house, and all those sorts of things. If the room you're subletting out is furnished, you can also charge a bit extra too.

I'd start by looking on Craigslist for properties similar to what you're offering in your area, see how much they cost, and then figure how much you need to rent that room out.

Jam it back in, in the dark.