Continuous rotation servos can be made from standard servos. Perhaps most important, they are now being sold commercially by at least one vendor for the robotics trade (Hitec).
One could also envision a series of gears or levers too, but that approach would be complex and more demanding from a design and construction standpoint.
John
Edit: Steppers are only one way to do it. There are plenty of DIY CNC with ready made applications using them, which made them attractive. Continuous-run motors, as long as you have feedback, will work fine. If you use a worm gear, they are self holding, and with DC power, overrun would be quite minimal, which might negate the need for a brake.