Asheville is nice but hilly. Good trails and lower Apps terrain.
Fayetteville (Arkansas) is nice too but not much for variety. There are some nice trails through the wood there. I would rate it as slightly above average for running.
Bervard, NC is pretty good too. Lots of trails and dirt roads. I think there is a small school there.
Stillwater, OK (OK State) is nice as well. They have miles and miles of dirt roads right off campus and a wonderful XC course. It's hot like Austin but not quite as hot and have way more trails and dirt roads on or near campus. In fact, I remember Austin being mostly asphalt or cement...
Flagstaff, AZ (Northern Arizona) is one of the best places in the country. Tons of dirt. From the FUTS to the forest roads to Buffalo Park.
Tallahassee, FL (FSU) is also really nice. The campus running is... average at best, but a short drive gives you a plethora of great options on hills and dirt. Again the heat is a problem here.
Portland (U of Portland) is pretty sweet too. I love Forest Park and it's a short run from UP's campus. I forget how many miles of trails there are in the park but it's more than you'll run in one long run for sure.
Rochester, MI (Oakland University) has some good dog parks that have trail networks and then the Paint Creek and Clinton River trails. Plus the Urban Parks and dirt roads near Shelby Township.
Boulder, CO (Colorado) is great too. I liked the trails going around and up to Green Mountain. But you could read Running with the Buffs to hear about the trails there.
Ogden, UT (Weber State) actually has some nice trails on Mt. Ogden and there abouts. The Mt. Ogden Rec trails are good for 10-12 milers and the trails up to and near the dam are pretty good too. It gets pretty hilly in Ogden though.
Ely, MN (Vermillion College) has some nice trails through the Boundary Waters Canoe Areas. The roads around the lakes are pretty nice for long runs too.