The candy thermometer is probably the single most important piece of equipment for the home confectioner. Many recipes require candy to be cooked to a specific temperature in order for the candy to behave and set properly. Although it is possible to make candy without a thermometer using the cold-water method, a thermometer makes things infinitely easier, and can be purchased cheaply at most major grocery stores in the baking aisle. If you will be making candy frequently, it is a good idea to invest in a high-quality thermometer.
The most important thing to look for in a thermometer is a side clip that allows it to attach to your saucepans so that your hands remain free while making candy. You want to attach your thermometer to the side of the pan with the tip fully immersed in the candy, but not touching the bottom of the pan.