There are some pretty inexpensive Chinese made temperature controller in evilBay. I just bought one, and it looks good so far, but I haven't given it a thorough workout yet. My gut feeling, however, is that it's going to be able to provide dead on accurate temperature control. Most items like this seem to be rock solid, and the technology is old enough that it's not hard to get right.
If you aren't comfortable with the electronics PM me and I'll try to work out some details for you, so long as you promise to return the design for my part to the community. Kind of a Hardware Open Source design. I'll put this on your site, too.
Hi posted a quick note on your homepage, I am a computer scientist (actually holds a Ph.D. in computer science (you all know that BS stand for bull sh%t, Ms for More of the same Sh%t, and Ph.D for Piled higher and Deeper

) but I do some small projects programing and controling electronics (robots, weather stations, video, alarms....).
I would really suggest that this kind of project is done using Arduino (
http://www.arduino.cc/), its an open source electronic design were a full control ship cost around $20 (depends on how many you buy). The arduio is also very easy to program, all the hard "fluf-fluf" is taken away and its very easy to control and read from the hardware.
Actually i have already done some design drawings for a fully automatic processor using a ardunio board, so i will just out line quickly what could be done, and the cost.
Arduino Pro 328 - 5V/16MHz - $19.95
One Wire Digital Temperature Sensor - DS18B20 - $4.25
(accuracy is from –55°C to +125°C (–67°F to +257°F) ±0.5°C accuracy from –10°C to +85°C)
A programable motor drive, like a 15A IRF7862PBF which cost $39.95
It should also be said that its possible to use step drives, they are weaker but you can control them to a fraction of a degree (but I personal dont think that kind of accurate is needed)
then of course the pump, a motor to drive the tank, some mosfets to control the pump and motor, a heating unit (to heat the bath), wires, and buttons and control stuff. The good thing is that to program all this is very easy.
Actually its very easy to program in different programs, make the programs editable. Its even possible to add alarms for water leve, if the tank stop rotating, temperature levels.
There are even displays (even touch screens but we should not go there, they are a pain in the a%% to program) that can very easy to be added so the process can be tracked.
The program running on the Arduino can very easy be updated using a usb cable connected to a computer. It would even be possible too make it possible to control the unit from a computer, loggin rotations, temperature ....., i have even built programs running on my iphone communicating with a arduino board (cant say more because i developed it for a company and I signed a Non-disclosure agreement)
Just to show of some videos that is in the area of such a machinen
Ardunio driving a motor
http://www.youtube.com/watch?v=1Avm4blyp7Y
Ardunio driving a pump system
http://www.youtube.com/watch?v=ELLUB81m5Z4
Ardunio temperature
http://www.youtube.com/watch?v=iypt-Y4ytac
Ardunio temperature logger
http://www.youtube.com/watch?v=_sH5kaKO8Vw&feature=related
Ardunio controlling a Mosfet
http://www.youtube.com/watch?v=JC9qeVjnScA&feature=related
iPhone controlled garage door opener using Arduino (but this uses a webserver which is not really like running it native on the iphone, he could run it from any computer)
http://www.youtube.com/watch?v=V8UV2BtndW8
iBot - a real iPhone robot made with Arduino
http://www.youtube.com/watch?v=mi3kmdcAXMU&feature=related
Well, you might ask if the platform is fast enough to respond, well, people have written helicopter stabilizer and stuff, but I think this is the best to show of the speed
(just remember that if the power were on all the time the magnet would hit the coil, if its off to long the magnet would be out of reach to pull back..)
Just remember this kind of programing will take some weekends to wire together and program, but its not more. The accuracy will be either the same or better then Jobo (it comes down to how the temperature sensors are placed also and the flow in the tank).
I have even made a design skiss of a fully automatic system, including a lift, motor and pumps to replace a ATL system, but haven got around thinking of the hardware design.
if you are interested shoot me a PM and I give you my private email.
cheers
(sorry for the english, its not my first language)