you probably know this already:
turn off push in mail ( settings > mail > fetch new mail ) and set the schedual to hourly or manual – manual will only get mail when you open mail, it will also control the updating of calendars and contacts 
turn off push in facebook ( settings > facebook )
turn the screen brightness all the way down ( i leave auto brightness on – it probably uses more battery, but i still need to see
turn wifi off if you arent using it ( settings > wireless )
turn off 3g if you arent using it ( settings > general > network > 3g )
tuen off bluetooth if you arent using it (settings > bluetooth )
turn off indexing ( settings > general > search ) untick the ones you dont want indexed – i never use the search, not even on my mac – i know everything that i have on my machines, and i know where to find it.
put the autolock on. ( settings > general > autolock )
one feature id love to see is auto 3g toggle (so that it automatically comes on if you need it) and power profiles ( so that you can save a configuration as “max battery” and switch by double clicking the button
maybe there is an app ( there is probably a jailbreak app for it )
