Hmm, is it really correct that you do not need any current limiting when using steppers with a L293D? I tried to use a similar setup as dutchboy, a power supply with 12V and 1.5A. But the L293D become verry hot after seconds and the stepper doesn't work correctly after some seconds. So I reduced the input current to 600 mA and now it works. But perhaps it is only necessary to use a heatsink.