Today, in our Linux Page (in Spanish) we strongly suggest a very useful applet for every Gnome OS: GSA. The Gnome Sensors Applet let you constantly check the hardware sensors, including CPU temperature, fan speeds and voltage. GSA is very easy to install and manage; its intuitive graphical interface allow you to decide what alarms you prefer to display in case of emergency. GSA is recommended for all the Linux users who constantly push the limits of their pc. 
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OOooh. Overclocker’s paradise. Is gpu, north bridge, hdd, and ram in there, too?
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Yes they are. hddtemp is required for the hdd temp and if you have an Nvidia card with the drivers installed, it’ll show that too. It can show everything if you have google help you. I don’t know of any RAM that has a temp sensor in it but CPU and GPU were running already without any extra work on my part.
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You can also install libsensors to get all the voltages, fan speeds, and temps of a few chips on your board. After installing, run libsensors from terminal to see what they correspond to. You may have to restart your system before they will work in the sensor applet.
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