If you don't need infrared support, disable it in the BIOS or shutdown the IrDA device driver. There are also some IrDA features of the kernel which are useful for saving power. In the specifications of my HP OmniBook 800 it is recommended to turn off the IR port, if it is not in use, because it may consume up to 10 percent of the battery time. If necessary, you may also try to disable the Fast RRs feature in the IrDA section of the kernel. This option will give you much better latencies but will consume more power.
PCMCIA services consume much power, so shut them down if you don't need them.
I'm not sure to which extend the backlight consumes power. WARNING: AFAIK this device can only bear a limited number of uptime circles. So avoid using screensavers too much.
For some examples to build batteries with increased uptime up to 8 hours look at Adorable Toshiba Libretto.
For information about APM look at the APM chapter above.
A hacked rclock. Booker C. Bense has hacked the rclock program to include a simple battery power meter on the clock face.
xbatstat. A battery level status checker for Linux and X.
KDE provides KAPM, Kbatmon and Kcmlaptop. Written by Paul Campbell kcmlaptop is a set of KDE control panels that implements laptop computer support functions, it includes a dockable battery status monitor for laptops - in short a little icon in the KDE status bar that shows how much battery time you have left. It also will warn you when power is getting low and allows you to configure power saving options. Similar packages you may find at the GNOME project . See the software maps at both sites.
Please see Battery-Powered-mini-HOWTO for more information.
toshiba-fan Turn the fan on a Toshiba Pentium laptop on or off. This is a command line utility to turn the fan of a Toshiba laptop on or off, or view its current state. It should work on all Toshiba Pentium laptops that have fans.