This is somewhat related, but if it is too off-topic please move or delete...
Regarding the magnetic stirrer from a cpu fan plans all over the place, I encountered problems overcoming the coupling of the magnet and the stir bar and with the added magnet's attraction to the permanent magnets in the fan motor. So after that letdown, I scaled up to a leaf-blower motor which works well enough I suppose but is really tall (is from a plug-in style blower, so has a transformer attached...) The question is how to control the speed if wanting to use AC, but my search has been less than productive. Tried to use a dimmer switch, that didn't work...read about rheostat and variac design, but prefer chemistry to thousands of tiny puncture wounds from winding, stripping, etc. As of right now, the variable DC output from a model train control box is seemingly adequate, but am I destroying the longevity of the motor or anything? Also, since using DC, isn't the transformer kind of extraneous? Don't like the tall stir plate because it makes everything less stable and forces the reaction vessel to be placed higher up which is more stressful for the experimenter...
very much agree with Vesp re: goodwill-type stores, bought a rice cooker for 2.99, and old self-heating thermos for 1.00 which were promptly upgraded/altered to make nice oil bath and hotplate... 

The trimmer motor will run on DC without a problem, and the way to adjust the speed is to change the voltage. The only trouble with using it is that it's way more powerful than you need, and you may have trouble getting it to run slowly enough. Without speed control the things going to run at 10, maybe 20,000 RPM or so.

Similarly the water heater heating coil is way overkiill. It would be like using a washing machine motor for an overhead stirrer!  I believe that the heating element would be very difficult to control, and without good temperature regulation is would boil away your oil and melt itself down. Washing machine motors weight, what?, 15-20 lbs.? They're big, too. There's no easy way to regulate the speed, which would be synchronous with the 60Hz AC input. There's a formula for calculating the speed, but you have to know how many poles the motor has, but I expect it would run at about 120 revolutions per second.

There are several problems with using a computer fan to make a stirrer, especially if you use magnets out of a hard drive. You can't use just one because they have their poles on the flat sides. (I guess if you could stand them on end it would work.) Because of that you have to use two, and that puts a hell of a load on the magnets built into the fan motor, making it hard to start rotating. The good thing about these little motors is that you can control the speed by varying the voltage, so if you could get a better magnet, like alnico, it might be feasible. The other thing about the rarre earth magnets from hard drives is that they go dead very quickly if exposed to heat. Overall I don't think the PC fan is a very good solution unless you are going to use it alone--no heat.

I like Sedits idea with the show cooker. I forgot what you called the stuff you plastered over the wire with, but what is it and where do you get it?

The stirring hotplate I made was built from an electric frying/double boiler/deep fryer all in one. It's made of aluminum and has one of the big heating elements formed into a ring and stuck to the bottom rather than nichrome zigzagging all over the place. That gave me a place to attach the magnetic stirrer, which is made from the motor out of a hair dryer. These can run on DC, and by connecting the power through a 100 Ohm potentiometer you have an easy way to control the speed. I use a 7V DC transformer for power to the stirrer. Another benefit of using the hair dryer motor is that most of them have a plastic disk attached that acts as a fan to cool the motor. You need it anyway, but it's also a good place to glue the magnet.

The heart of the cooker is the piece that contains the heating element, and it's got one of those large black plastic thermostats that plug into the front of the pan. I use it to hold an oil bath all the time, and the thermostat will hold the temperature constant within a degree or two of where it's set.

PP