Here's a previously unused 120mm 12v pc fan...two rare earth magnets mounted to the hub...and the whole thing mounted in an old plastic terrarium from when the kids were small.
The stir bar is a couple of small magnets, a couple bits of 1/4 inch dowel, all surrounded with some sugru.
As you can see, above, it works.
Here's a picture without the flask...you can see the magnets and the cool sugru bar.
