Control of Stepping Motors. A Tutorial by Douglas W. Jones.
Unipolar Stepper Motors and Control by Rustle Laidman
Nuts And Volts Magazine (Oct 1998). Build This Stepper Motor Controller (PDF).
A large collection of links about stepper motors at EDUCYPEDIA (The educational encyclopedia).
Stepper Motor Sequence Generator (probably the simplest 2-phase full step sequencer circuit).
Working With Stepper Motors
Stepper Motor Driver (74LS194).
Stepper motors. Stepping your way around...