There are two large airports serving the Provence: Marseille-Marignane and Nice-Côte d'Azur. You can fly non-stop from the US to both airports. You can check with the usual suspects, like Expedia, Orbitz, Travelocity, which do not include low cost carriers' flights. British Airways normally has good deals for those flying in from North America, Australia and Asia, that is if you can stomach London Heathrow's chaos and BA's dismal baggage handling record. Coming from the US the next best thing to flying directly is to go through Brussels or take a flight to Paris and the TGV high speed train down to your destination in the Provence.
There are many low cost carriers flying to Marseille, Nice and some of the smaller airports, like Nîmes, Toulon and Avignon. Ryanair has established a hub in Marseille in 2007. Ryanair, Easyjet and Air Berlin have the most extensive network and fly year round. Some of the smaller airlines have service only during the tourist season. Here is a short overview of what low cost airline flies to what airport (as of May 2009). As the smaller budget airlines change destinations once in a while or have only seasonal flights, you might want to check with farecompare.com, flycheapo.com or Microsoft's Bing Travel (the former farecast.com), just click on the links below. Flightstats.com, a brand new website, aims to track flights as well as airline's historic pricing during past seasons - quite useful if you are flexible with your travel plans.
The Avignon-Caumont airport, 8km east of Avignon-Centre is tiny, modern and cute but there are persistent rumors that Avignon's Chamber of Commerce, which runs it, might close it. Very close to Autoroute A7.
Flybe (Southampton, Exeter)
Marseille Marignane Airport
The Marseille-Marignane airport lies 27km northwest of Marseille Centre with easy access to the Autoroute A51 leading north to the east/west Autoroute A8. In other words you don't have to drive through Marseille to reach your final destination in the Provence. The airport has ample services and an excellent website, check here for the many airlines flying to and from Marseille.
A small airport in the Languedoc but close enough to the Western Provence to be taken into consideration. Check the airport's rudimentary website, which fails to mention that Easyjet, Ryanair and Sterling have regular flights to Montpelier.