I'm using the bipolar circuit on http://arduino.cc/en/Tutorial/MotorKnob - same hardware, and a separate 12v battery for motor supply. The motor (from an old Epson Stylus, 1.8 degrees) was working very well - massive torque.
Then I fiddled with my sketch (I'm using the AccelStepper library) - but the strange thing is that the motor is not rotating properly now even after I commented out all my changes. And there is no torque at all. Both coils still give me 8 ohms as before. And I have connected a PC speaker to be able to "hear" the pulses - all four pins to the motor are pulsing.
So I assume that the motor is still ok, the chip/Uno are still ok - and it must be wiring order that I've messed up? But I've tried several wiring combos with no change