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1. Defrag regularly -  The faster your hard drive does its work - less demand you are going to put on the hard drive and your battery.  Make your hard drive as efficient as possible by defragging it regularly. (but not while it’s on battery of course!) Mac OSX is better built to handle fragmentation so it may not be very applicable for Apple systems.

2. Dim your screen - Most laptops come with the ability to dim your laptop screen.  Some even come with ways to modify CPU and cooling performance.  Cut them down to the lowest level you can tolerate to squeeze out some extra battery juice.

3. Cut down on programs running in the background.  Itunes, Desktop Search, etc.  All these add to the CPU load and cut down battery life.  Shut down everything that isn’t crucial when you’re on battery.

4. Cut down external devices - USB devices (including your mouse) & WiFi drain down your laptop battery.  Remove or shut them down when not in use.  It goes without saying that charging other devices (like your iPod) with your laptop when on battery is a surefire way of quickly wiping out the charge on your laptop battery.

5. Add more RAM - This will allow you to process more with the memory your laptop has, rather than relying on virtual memory.  Virtual memory results in hard drive use, and is much less power efficient. Note that adding more RAM will consume more energy, so this is most applicable if you do need to run memory intensive programs which actually require heavy usage of virtual memory.

6. Run off a hard drive rather than CD/DVD - As power consuming as hard drives are, CD and DVD drives are worse.  Even having one in the drive can be power consuming.  They spin, taking power, even when they?re not actively being used.  Wherever possible, try to run on virtual drives using programs like Alcohol 120% rather than optical ones.

7.  Keep the battery contacts clean:  Clean your battery’s metal contacts every couple of months with a cloth moistened with rubbing alcohol.  This keeps the transfer of power from your battery more efficient.

8. Take care of your battery - Exercise the Battery.  Do not leave a charged battery dormant for long periods of time.  Once charged, you should at least use the battery at least once every two to three weeks. Also, do not let a Li-On battery completely discharge. (Discharing is only for older batteries with memory effects)

9. Hibernate not standby - Although placing a laptop in standby mode saves some power and you can instantly resume where you left off, it doesn’t save anywhere as much power as the hibernate function does.  Hibernating a PC will actually save your PC’s state as it is, and completely shut itself down.

Add more RAM - More RAM means the computer will access the hard drive less frequently, and the hard drive uses much more power than your RAM sticks. 

Dim your screen - Those big, "ultra-bright" displays really suck down the power. Dimming your screen just 20 percent can add a good chunk of time to your battery life.

Unplug external devices - Anything plugged in via USB, FireWire, or PC Card/ExpressCard draws power from your computer. Yes, even your mouse. And of course, turn off your Wi-Fi radio when you don't need it.

Minimize CD/DVD use - Optical drives are probably the worst offender on your notebook when it comes to battery use. Unless you're watching a movie, don't even leave a disc in the optical drive, as Windows loves to occasionally read it, just to check on things...