What sized steppers are you driving? Do you want to build from scratch or purchase a complete drive module? If you want to build a stand-alone driver, you may use an L298, L6203 or L6204 driver coupled to an L297 translator.
**broken link removed**
If you're feeling adventurous, you can hookup a pair L6203 drivers directly to a 20Mhz PIC18F873 and have the software control the current as well as switch the phases to move the motor. Below is a schematic of a microstep driver I once built. I no longer have the code that runs on it however. It uses the 2 channels of PWM of the PIC16F873.