System Monitor Indicator is a new appindicator that displays your system CPU and memory usage on the panel - be it the regular Gnome panel or the new Unity top bar.
The info is displayed directly on the panel, without having to click anything. This may not sound like a good idea if you use a netbook, but if you have a 20'' or larger monitor, you probably have plenty of space on your top panel.
Maybe some option to display the info in a drop-down or chose what info is displayed (with the other being displayed upon clicking the appindicator) would be nice though. But this is the first System Monitor Indicator release so it has plenty of time to improve.
The System Monitor Indicator developer welcomes all ideas / suggestions so if you have an idea for a cool feature, leave a comment! Or submit a bug.
System Monitor Indicator is available in a PPA but for Ubuntu 11.04 only so if you use Natty already, simply add the PPA and install "indicator-sysmonitor".
For Ubuntu 10.10 (I've actually only tested it in Maverick), simply download and install THIS deb file (for both 32bit and 64bit).
Want more AppIndicators? See here.