Being on a coast is the best place to be, imho, to consistently find a ~5k mile run. Generally speaking, I'd look on CO.com for transcons via IAH. There is no magic bullet, as load factors are high and fares are too this December.

I'd say play with some west coast cities on CO.com (LAX, SAN, SFO, OAK, SEA, PDX, ONT for a few), especially via IAH if you can find it. Ideally, leave during the day and take a redeye back. Those are the basics.