Which you choose depends on factors like your expected maximum and minimum temperatures the accuracy you need and your environmental conditions. The answer is a data acquisition interface with suitable software. The interface hardware might be a card which plugs into the expansion slot of your computer. You wire the sensor to the card and the computer can now monitor temperatures. It's best to choose a card that is specifically designed to cope with temperature measurement such as the Microlink 552.
Thermocouples are popular temperature sensors because they are cheap versatile and sturdy.
They consist of two dissimilar metals joined together making a continuous circuit. This voltage varies with the temperature difference between the junctions. If the temperature at one junction is known the temperature at the other junction can be calculated. There are several types of thermocouple labelled with letters according to their constituent metals. A K-type thermocouple for example is made up of chrome and Alumel.