Create a robot arm using microcontroller
You might get more mileage out of a high torque servo at first.  Servos have their own control circuitry so all you need to do is give them a command.  Stepper motors are good, but perhaps you should save them for future development as you'll probably have a lot of effort just making the mechanics of the arm and handling anything unforeseen that comes up.

Servos are either controlled digitally or via a pulse width.  The pulse width control is easy - the length of the pulse determines what angle the servo sets itself to.  I haven't yet worked with them but from what my project partners tell me it's between 1ms and 2ms pulse width for the full range of motion and the pulses need to come every 16ms This makes choosing a microcontroller easy - it just needs to have a timer/counter module with output compare.  You won't have to worry about powering the motor through the microcontroller because the control pulse doesn't power the motor.  

You'll need to judge the amount of torque necessary for the servo depending on the weight of what it's moving, and the amount of time it takes to travel a full 180 degrees (or whatever its full range is) is also important.  The servos seem to operate at 4.8V or 6V so that's a consideration.  Here's a page with some hobby servos to buy: http://www.servocity.com/html/hitec_servos.html

You may or may not need high-torque, but that should at least get you started and send you in the right direction.