Magnetic stirrers are extremely useful to have around your lab (Or kitchen) at times, whether you're mixing chemicals or chocolate milk. Industrial magnetic stirrers are often rather expensive though, so here's how to make a cheap one using 2 hard drive magnets, a computer fan, superglue, a wall wart (Or batteries) and a casing.
First thing is to superglue the hard drive magnet to the center hub of the fan. This may take a bit of experimenting to find the center, so the fan won't wobble apart. One it's found, make sure the magnet is glued on well and then place the second magnet on top of it, like in these two pictures:
Then place spacers on the corners of the fan slightly taller than the two stacked magnets, so you can fir the top of the casing on to the fan.
Superglue it all in place, wire in the wall wart (I'm using an adjustable one, anything from 5-10 VDC should work fine). You may need to use a potentiometer to adjust the speed of the fan.
Put the casing back together, and you're done. For magnetic stirring rods, try the shaft from a small DC motor, such as one you'd find in a CD drive or other such device.