I think the most popular one for calculating distances is Great Circle Mapper. It can also draw a range circle from a given point (i.e. 5000mi@ORD).

But if you are looking for an actual list, probably easiest to download the United Timetable in PDF, which shows mileage to each destination on the current schedule.

Of course, this gets complicated by routing, which can significantly lengthen the distance flown, versus "the way the crow flies."