I was looking for a lightweight, easy to use systems performance log for a Debian 5.5 server and came across Webminstats
Systats is a Webmin module that tracks cpu, memory, disk and io statistics over time.
It doesn't install without a few additions to the standard Debian install.
Of course you need Webmin installed, and then perl. Once you've installed Webmin and perl on your systems, run the following command lines (as root or sudo) in your shell BEFORE you attempt to install systat:
apt-get install rrdtool
apt-get install librrds-perl
apt-get install librrdp-perl
apt-get install libwww-perl
Once these packages and libraries are installed, download the webminstats .tgz file from http://sourceforge.net/projects/webminstats/ onto your computer.
Then, install that file through the Webmin module installation interface by telling it you want to install a Webmin module from an uploaded file, then point Webmin to the file you just downloaded.
Restart Webmin, and watch the magic happen.