One of my favorite sites for checking new installer apps is called InstallerApps.com. Recently the author did a great post on how to save your battery life. This article is specific toward iPods, but they can also be very helpful to iPhone users.

For me the three biggest tips are Less Email Addresses, Turn WiFi Off and Turn SSH Off. The reasons I think these are the three biggest is because they all have to do witch checking things while it is in sleep mode. It is always checking for wifi, always ready for SSH and always checking your e-mail. The less you can make it do these things, the better.

Here is the full 10 Ways to Increase your Battery Life by Installer Apps