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/
I think I'd like to try to build one of these just for fun. Using liquid yeast is new to me and this would probably be a nice enhancement to the yeast starter.
<= scratches his head and wonders what stuff to get... lol