A few things you can do;
Forget about battery booster apps. (they'll be running all the time also)
Disable your "auto-sync" and "auto-updates", or set them to run at longer intervals. Or even "manual". This includes widgets (weather widget, news widgets, etc)
If you have apps you no longer use, uninstall them. Some of them don't like to give up without a fight.
Screen brightness, you can set manually, especially indoors where you don't need it as bright.
Settings/Applications/Manage Applications will tell you which apps are currently running. You might be surprised. I have a file manager that seems to always be running, although I don't use it often.
As for more drastic measures, you can flash a custom ROM. Some of the better custom ROMs will improve battry life.