I just did another Instructable - Easy, Reversible Motor Control for Arduino (or any Microcontroller) (wow - that's a mouthful...).
It is the result of my effort to come up with something less annoying to construct than an H-Bridge - using just locally available parts in the process (under $9 at Radio Shack!).
If you order components online - you can get the cost down around $4 each. Pretty good considering it can handle 5 amps.
I find documenting projects online highly satisfying. It lets me set aside worthwhile projects that I've gotten bored with - without feeling I'm abandoning them.
This particular Instructable is hypothetically a subcomponent of an upcoming homebrew CNC system.