There are a plethora of amazing hardware monitoring programs available free of charge online.
I personally prefer NZXT's CAM Software, but I may be bias considering my CPU Cooler must be controlled by it. Nonetheless, it is one of the easiest temperature monitoring applications I've ever used.
NZXT CAM: https://camwebapp.com/
A few perks of CAM...
1. Not only can you monitor CPU, GPU, and RAM temperatures, you can also monitor usage.
2. CAM comes with a Fraps like FPS counter that can display your current, average, and max FPS count in game.
3. If you happen to purchase an NZXT product in the future, CAM can easily connect to and control said item, such as the GRID or HUE +.
If you're looking for something simpler, I also use Hardware Monitor.
Hardware Monitor Download: http://download.cnet.com/Open-Hardware-Monitor/3000-2094_4-75217106.html
The temperatures are harder to read, but it doesn't use as much RAM as CAM. You can also control your GPU fan in this program.