I envy you, you're going to have a great time. A few places I remember..
Aix en Provence itself is a great city for walking around, stopping at cafes, people watching, etc.
The Luberon range, which is not too long a drive north from Aix if I remember right. There are some very picturesque cities perched on the hillsides, with the older town in ruins high up on the ridge, and the newer towns down below. You can usually hike up to the ruins. Some of the town names (if memory serves): Bonnieux, Menerbes, Oppede le Vieux, and La Coste (famous for the ruined chateau of the Marquis De Sade).
Pont du Gard, an old roman aqueduct spanning a beautiful canyon. It's probably quite a ways west of Aix though and you can't walk over it anymore like you used to be able to do. The engineering of this edifice is amazing for the time period it was built in. I remember having a traditional picnic here with wine, cheese and a baguette.
You're going at a good time too, the crowds should be thinner and the vineyards may be beginning to change to autumn colors.
If you can rent a bike, the whole area is great for biking - hilly, but the views and charming old towns are worth it.
Have fun and tell us about it!
- John T.