Is there an indicator (a.k.a applet, launcher) that I can embed to my gnome panel which shows my cpu, gpu, hdd etc. temperatures?
sensors-applet will do the trick for you. You can install it with:
sudo apt-get install lm-sensors sensors-applet
You should then do
sudo sensors-detect so that lm-sensors is configured (it will scan sensors in your hardware).
Then simply add "Hardware Sensors Monitor" to the panel. Then, within the context menu, you will be able to configure which sensors will be shown, units, update interval....
sudo apt-get install sensors-applet
Then when you right click the panel, and go to "Add to panel..." and add a "Hardware Sensors Monitor", you'll see something like this:
And yes, as luri points out, you'll also need to set up lm-sensors for this:
sudo apt-get install lm-sensors sudo sensors-detect
Go through that and find out what modules need adding (you can have it write to modprobe directly in the last step) and then you should be good to go.
sudo add-apt-repository ppa:alexeftimie/ppa sudo apt-get install indicator-sysmonitor lm-sensors indicator-sysmonitor
I like it more for the simplicity.