Each EasyDriver can drive up to about 750mA per phase of a bi-polar stepper motor. It defaults to 8 step microstepping mode.(So if your motor is 200 full steps per revolution, you would get 1600 steps/rev using EasyDriver.) It is a chopper microstepping driver based on the Allegro A3967 driver chip. For the complete specs of the design, read the A3967 datasheet. It has a variable max current from about 150mA/phase to 750mA/phase. It can take a maximum motor drive voltage of around 30V, and includes on-board 5V regulation, so only one supply is necessary. The best part - low cost. The parts cost is maybe $10, less if you make the board yourself.
-- above text and all designs are from Brian Schmalz's Project page.