Just east of Flag on I-40 is Walnut Canyon National Monument (I think it's a monument). It's a small park of Indian ruins/cliff houses, with a trail and visitor center/museum. very cool, and very easy to get to and see.
When you go thru Sedona, you'll want to drive up to Flagstaff through Oak Creek Canyon on Hwy 89A. Very pretty drive. There's some nice stuff to see (country) around Sedona also. A short drive up Shnebly (sp?) Hill road may be fun.
Going out of Flag, drive Hwy 180, its the prettiest way. Watch for elk along the road, there used to be tons of them. If you have time, north of Flag on Hwy 89, there's another National Park or Monument called Wupatki, it's Indian ruins in very good shape, on a longish loop road.
Along I-17 going north, just up from Camp Verde is a small spot called Montezumas Well, a very small Indian ruin site around a natural water hole/sink hole. There's also Monteumas Castle, close to the Interstate as well. Fort Verde Hist site is also interesting, if you like that sort of thing, and fairly small scale.
You could google image search those places and get an idea what they look like, and if you'd be interested in seeing them.
If you had time, there's a lot to see in the area, those are some of the easiest ones. I lived in Flag for 8 years. Nice country, if a bit crowded now.