I built this stir plate awhile back using a 110v muffin fan, rare earth magnets, a small sheet of plexiglass and a dimmer switch for speed control. It has worked very well for me. Simple and effective.
These pics are kinda small for some reason. You can see the larger ones here: http://flickr.com/photos/33200128@N05/sets/72157612808063370/
These pics are kinda small for some reason. You can see the larger ones here: http://flickr.com/photos/33200128@N05/sets/72157612808063370/