uln2003 example
The ULN2003 and 2802 family of ICs are just lots of power transistors in one package. They are not specially for stepper motors, you can use them wherever you need to switch current on and off.
The reason you see them used frequently to drive stepper motors is that they have 8 or more outputs (8 for the 2003, 9 for the 2803) and as steppers need several current feeds, having them all in one device makes the circuit easier to build.
The only difference between each channel of a 2003 and using a single darlington transistor is that each of the output pins has a diode connected to it. The diodes are normally not conducting and are all combined to one pin. They are to 'absorb' the spikes you get from switching inductive loads so the IC and other connected equipment is protected. You don't have to use them, leave the pin open if they are not needed.
Brian.