Download 'Taskpanel' from marketplace. When you've used an app you want to stop from running in the background (NOT stuff that reminders and alarms require such as Calender, obviously, also probaly not Music etc), open Taskpanel, long-click the task, then add to autokill list.
Next time you turn the screen off (lock the screen) taskpanel will autokill the apps in the list (and will continue to do so every time they start, and the screen goes off).
Download 'APNdroid' from the marketplace and use it to turn 3G off when you're not using it (ie; when you're not browsing or whatever). DO NOT UNINSTALL THIS APP WITH 3G OFF since it'll mess your settings. It's a great little app though - put a widget on your home screen.
Turn off all the data syncs and sync manually when you want to check email/update contacts etc.
Turn off wifi and GPS (using the provided 'Switchers' when you're not using them).
Turn down the screen brightness to the lowest level you're still happy with.
If you do all that, you should find your battery life is massively improved.
Thx a lot!!!