Chartres may be your best bet if you intend to spend a few days, but to me it's not a place to spend much time. I strongly recommend at least one overnight because of the fabulous illuminations around town, which will be going on in September. The one on the cathedral is the most fantastic of them all, but we loved just about every one. In fact we couldn't stay up late enough to see them all.
As for nice villages, the area around there isn't that attractive. I look for interesting villages and towns everywhere we go, and I have nothing on my radar in that area. But there are people who know the area better than I do who may have suggestions. The closest thing to a village we've visited is Illiers-Combray, which seemed shabby to me.
On the bright side, an hour away is La Ferte Bernard, a lovely small walkable town with good restaurants and one great restaurant (Du dauphin), a river running through channels, a church known for its elegant carved stone letters, a great tea room, nice shops. Saturday it has a scenic market in the neighborhood of Saint Antoine church. With a car you can drive to a lot of beautiful villages in the area, especially if you go to the Perche.
Belleme in the Perche is another small town I'd recommend.
I don't consider Chartres a small town. Population 39k to me isn't small, but then I live in a rural area so my perspective is skewed. If you take the train there it might seem small, but if you drive there you'll realize its size--170,000 in the metropolitan area.
