Regardless of the sort of food you'll be creating this holiday season, you certainly don't want to under OR overcook your dishes. Use the right thermometer for the job, and count on perfectl feasts everytime.
Digital Remote Thermometer. $20-30 A probe connects to the digital unit that stays outside the oven. This makes it perfect for roasted dishes, i.e. your Thanksgiving turkey, as it prevents frequent opening and closing the door. Look for a magnetic back and a loud alarm.
Instant-Read Thermometer. $15-30
This models are designed to be inserted in your food to make sure it's cooked (or chilled) all the way through. They register quite quickly, but make sure you register the temperature from the center of the food. Perfect for grilled or pan-cooked items, and baked dishes like lasagna or even cakes. Look for digital models with a thin probe, and temperature registration from 20-350 degrees.
Candy Thermometers. $10-20
Long, traditional, analog (alcoholl)-based models that register temperatures up to 450 degrees. Useful for measuring temperatures of liquids, which makes them perfect for candy and jelly making, large batches of tea, or deep frying. Look for one with a sturdy clip for attaching to the side of a pot, and with a bulb that sits low on the thermometer, so you can take readings from short amounts of liquid.
There are other digital models, like thermocouple and infrareds (which are especially awesome, as they allow you to take the surface temperatures of cookware, grills, and griddles), but they are very expensive and unncessary for most home cooks.
And remember to take your food off the heat about 5 degrees under the desired temperature. The food will continue to cook as it rests.