I have built my 3D printer and opted for a PC laptop power supply
Its rated for 8A output.
you might want to look at the Reprap wiki again as you may find that the 24v is the stepper motor rating and not what is actually needed.
when playing around with steppers i found that you get a choice between torque or speed, increasing the voltage provides more torque but doesnt seem to make the motor perform any faster. i aslo ended up at a point where if i increased the voltage it made no difference apart from loading the current sensor circuit in my bench PSU. I got no where near 24v, the motors im using i think are 12v but running with the pololu ref voltage set for 3.5v ishhttp://reprap.org/wiki/Sanguinololu
in the end i bought all of my kit (sing-along-with-lulu board, 4 motors and the pololu stepper drivers) from think3dprint3d under the illusion that it would be plug and play.
to be fair it was pretty straight forward - the problems i had were more to do with setting up the mechanical accuracy of the axis.
As this is the arduino forum the Gen7 board is an excellent choice as it is built around our beloved chip.
anyways dont listen to me - Grumpy Mikes the dude