S.M.A.R.T. HDD temperature, too
When I installed Speedfan software to my children's computers I realized it allowed you to measure the HDD temperatures if they are SMART compatible (which they are). So I thought it would be nice too to have such info on my Ubuntu desktop too.
So I google for a moment to learn that hddtemp allows you exactly that: to measure your SMART-compatible HDD temperature from command line: just install it
sudo apt-get install hddtempand type
sudo hddtemp /dev/hda(or any other drive name you have). It works as expected and you may consider to run it as a daemon so you can use the nice Gnome sensors applet that does a very nice job of showing all the temperature (and fan info if you wish) collected by several means, including acpi, lm-sensors and hddtemp. It is not installed by default so you'll have to install it too.