I'm not as negative as Felicity about VRBO... at least at this point. As a renter, it was always my "go to" site when looking for rentals, both in Europe and the USA. But I've only been listing our Bonnieux apartment for three years and don't have as much history from the owner's perspective. We do get bookings through VRBO, so at this point it's working for me, but I'll continue to evaluate every year.
The other site Roz mentioned is
www.theluberon.com. This site has been around for 10+ years and used to be run as sort of an agency. The owner Paolo was a little bit active on slowtrav. Nowadays it's sort of a rent-by-owner site (really by owner, not agencies) with a bit of a twist. Paolo personally visits all the properties and decides if he'll list them. He takes all the photos and writes the copy. He's a great photographer (professional, I think) and a really good writer and web designer. He's got lots of area content on his website, which helps with his google ranking in searches. But inquiries come directly to the owner and all the transaction is between the owner and renter.
At the end of the year, on an honor system, I pay him 5% of bookings through his site. I seem to get quite a few bookings from Australia through this site. It's a beautifully presented site, but lacks some of the convenient features of VRBO. They don't have their own review mechanism (the owners provide reviews or he just gets mine from VRBO), and I have to email him with calendar changes. I actually keep my rental calendar on VRBO.
I know some tourism offices list rentals with a link to properties. I'm not sure if there's a listing fee involved. That would be another option, or perhaps to join up with other owners in an area to create a bit more of an internet presence. The challenge is to get high enough on a google search that someone can actually find your place!
I have used regional agencies before. I think you'll get the best prices if it's a small local agency that actually visits properties and can honestly represent them.... and doesn't have a lot of overhead.