Stepper motor - How to choose a driver
If the winding resistance is such that you generate the intended phase current by simply applying the rated voltage, then simple drivers like the L293D will be OK. It may well be, if you're unsure of the motors characteristics, or need to operate over a range of supply voltages that you need to either choose a driver that has some form of current limiting built in, or do that yourself externally.
  Something like the L297 can do this, and generate the signals needed for the output stage, or you can implement similar logic easily with separate components - a quad op-amp/comparator can do the same.