I really like finding little applications that do a single specialized task really well. In this case, it is a Dashboard widget called Deep Sleep that puts your computer into hibernation. I discovered it on MacOSXHints and have been using it regularly for a few weeks.
Mac laptops use three sleep mechanisms: Safe sleep, deep sleep and quick sleep. The primary difference between them is how the computer reacts when all power is removed. Safe sleep is the default behaviour and will resume normally even after the power source is completely disconnected (that means you can change batteries without fully shutting the computer down). Deep sleep also wakes normally (albeit more slowly) and draws no power at all. Quick sleep will not remember any data when started after a power loss.
The nice part about this widget is that it enables you to use the deep sleep method once, then have it revert back to the standard form afterwards. It is especially convenient for when you know the computer won’t be needed for a few hours, but you’ll need the full battery afterwards. This ability is also useful for when the battery has aged and no longer holds the original power (like mine).
So if you need to put your computer away for a while, but still want power when you wake it again, give Deep Sleep a try.