The diagram for controlling a unipolar stepper motor with only two pins (http://arduino.cc/en/Reference/StepperUnipolarCircuit) shows a forward biased diode on the common pin of the ULN2003 chip. Can anyone tell me why this diode is there? It seems to me that it would keep the chip's built-in back EMF suppression diodes from doing their job.
Indeed, it would seem that diode presents a problem.
I wired it up without the diode, and it seems to work fine. I also removed the two superfluous 1K resistors on the left and it still works fine. (The ones on the right of the chip definitely are neccessary.) I'm using a UNL2803 chip instead of the ULN2003, but that shouldn't make a difference. I must be missing something. 
Please do not cross post, I answers this in another thread yesterday. >:(
Who's cross-posting? Why didn't you answer it in this thread instead yesterday, since I asked the question 3 days ago?
Grumps, you need to lighten up and get someone to explain the meaning of "cross posting" to you. Sheesh. >:(