The list JHS linked above is an excellent start -- there are other wedding venues listed as well under the venue section, so it's worth venturing beyond that Top 20 list. (And or course, even the venue section is not complete).
As JHK posted above, Le Mas du Pierre has some excellent food and the grounds are lovely (although not fully countryside). It's located just outside of St. Paul de Vence. It's also convenient to a well connected airport. (I have not been to a wedding there, however)
It's a bit outside of your target zone, but I attended a very nice wedding at Le Chateau de la Messardiere in St. Tropez. Each guest had their own suite.