Use a recent 'tickless' kernel (like in Fedora 7 for i386). It saves at least some Watts.
Configure non-root-disks for spindown.
In file /etc/rc.d/rc.local (replace ? by relevant disk!)
*** Addition ***
hdparm -S60 /dev/sd? #Spin down after 5 minutes of non-use
*** End of addition ***
In file /etc/smartd.conf
*** Replace ***
/dev/sd? -d ata -H -m root
*** By ***
/dev/sd? -d ata -H -m root -n standby
*** End of Replace ***
You should also delete the 'auto-generated' tag in front of the file.
If you are satisfied with a slower startup of your audio (yes easily) and it is a snd_ac97_codec compatible soundcard, you can save 1 entire Watt with the following:
In file /etc/modprobe.conf
*** Addition ***
options snd_ac97_codec power_save=1
*** End of addition ***
Use the 'Blank Screen' screensaver instead of f.i. flying pinguins.
(For laptops) Switch off wireless and bluetooth connection when not in use. Most likely (not always) possible with a keystroke-combination indepentant from the operating system.
