Air bnb, trip advisor, VRBO, Homeaway are great.
If you want to go into it as a legitimate business I know a lot about it because that's what my uncle does.
He bought houses in London before the economic crash and now let's them as 'guest rooms' on that website. Each house has 4 rooms or so.
The amount he makes on there from those rooms is fukking disgusting.
Its a good hustle. Many people in the holiday letting business became millionaires of it.
My uncle always told me property is the quickest way to make a million. I'm beginning to believe him. So many areas of exploit.