A good thermometer. I use a Polar Ware thermometer like the one to the left, but I have also had great success with digital thermometers as well. The reason a thermometer is so important is that two of the most fundamental traits of good cheese, acidity/sharpness and texture are directly related to specific temperatures. So the only way to even have a chance of predicting what the end product will taste like is to use a good, accurate thermometer. The method I use to calibrate my thermometers is called the 'Ice Point Method':
Fill an insulated cup with crushed ice and water.
The cup must have enough crushed ice to provide an environment of 32°F, so you may need to pack more ice into the cup during the process.
When the mixture of the water has stabilized in about four or five minutes, insert the thermometer to be calibrated to the appropriate immersion depth.
Be sure to hold the stem of the instrument away from the bottom and sides of the container (preferably one inch) to avoid error.
If your thermometer is not accurate within +/- 2°F of 32°F., adjust the thermometer accordingly. The ice point method permits calibration to within 0.1°F.
You can find more information at http://www.allfoodbusiness.com/calibrating_thermometers.php .
The second piece of equipment is a large, non-reactive pot. Basically, to be on the safe side since acidifying milk will sit in the pot potentially for several hours, don't use aluminum. I use an enameled pot that can hold a gallon and a half of liquid, and it works like a champ. It doesn't impart any flavors, it is really easy to clean up, and it heats nice and evenly. Stainless steel would work too, but many times they are more expensive. The particular pot I use I inherited from my grandmother, but I have seen similar pots at Ross/TJ Max for less than $50 brand new.