A Zoo-Med small size: http://www.petsmart.com/product/inde...ductId=2752652
All UTH's MUST be regulated by a thermostat. without a thermostat UTH's can and will get hot enough to kill your snake if they are not regulated. (130+ F) Here are some good thermostats, stay away from the junk sold in pet stores. They are overpriced and do not work well.
Budget: http://www.amazon.com/Hydrofarm-MTPR.../dp/B000NZZG3S
Mid-Range: http://www.reptilebasics.com/ranco-etc-111000-pre-wired
Best: http://spyderrobotics.com/home/products.html
Keep in mind that UTH's do NOT increase the temperature of the air inside a cage. This means that if the temperature of the room drops below 75 degrees you will need a heat lamp to increase the air temperature (preferably to 80 degrees). I would recomend an infrared heat lamp so it can be used 24/7 without bothering you or the snake.
http://www.petsmart.com/product/inde...uctId=11147193
For more info checkout this thread:http://ball-pythons.net/forums/showt...t-Thermometers
And this thread is also a good read: http://ball-pythons.net/forums/showt...ius)-Caresheet
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