For those not familiar with Psensor, this is a tool which can be used to monitor the motherboard and CPU temperatures, Nvidia GPUs temperature, (for ATI/AMD it's more complicated) hard disk temperature, fans rotation speed and CPU usage.

GNOME Shell CPU Temperature is an extension that displays the CPU temperature on the top bar. The extension is not new, but it never worked for me until recently when the extension got support for lm-sensors. 

These days we've got a lot of comments requesting for a temperature monitor applet with Ubuntu AppIndicator support that displays the CPU / Motherboard temperature, Fan speed, etc. on the panel.

Well, great news! Alex Murray has created an Sensors AppIndicator which can display various temperatures and fan speeds as well as the GPU / fan speed for Nvidia graphics cards (if you have installed the "nvidia-settings" package only!).

Indicator-Sensors doesn't have a PPA yet so I've debianized it and uploaded it to the WebUpd8 PPA so you can install it already in Ubuntu 11.04. But please note that Indicator-Sensors is currently in alpha so it may not work for everyone, or you may find bugs. If that happens, report any bugs you may find @ Launchpad.

Conky is a free, light-weight system monitor for X, that displays any information on your desktop. You've seen it in many screenshots under various forms; take a look at these screenshots if you don't know what Conky is.

To use Conky, you must manually set it up - and that's not easy as you must manually create the configuration file and customize it yourself. But now you can do this a lot easier using ConkyWizard, a GUI written in Qt and C++ to set up Conky and customize everything visually.

lm-sensors appears to have stopped working in Ubuntu Karmic Koala (basically for any distro running Kernel 2.6.31). If you look at your Kernel messages, you will see something like this:

ACPI: I/O resource it87 [0x295-0x296] conflicts with ACPI region IP__
[0x295-0x296]
ACPI: Device needs an ACPI driver