This is one of those hints that may seem exceptionally obvious to people, but may not have occurred to others: if you wish to conserve battery life on your laptop and don't require network access, turn off your AirPort card (which can be easily done via the menu extra).
[robg adds: Yes, it's obvious. It's also easily overlooked; I switched mine off this weekend while writing some stuff, and probably gained 20 to 30 minutes of useful battery time...]
Mac OS X Hints
http://hints.macworld.com/article.php?story=2003022623122998