Few things to help you manage your phone.
Anycut - I have a shortcut to battery details so I can see how the battery is doing.
Toggle - lets you turn different setting of and on from the same interface.
Locale - Can manage settings based on time, day of week, location, and more.
I'd download Locale, if you have a pretty regular schedule, you can decide what conditions you want set at certain times or even certain locations.
My locale default is to have Wifi and GPS off, but when I'm at home, the Wifi turns on so I can connect locally. Very handy like that.
In the settings menu there's a synchronization setting. it keeps gmail, contacts, and calendar up to date back and forth between the web and your phone. I have sync for my contacts disabled, as I don't really need them to be synchronized all the time. I may add calendar and do an manual sync at some point. I've noticed that if you're in the gmail app, and press menu there's a button to let you manually sync. If you don't want email showing up all the time, you could disable the auto-sync and just use that manual sync whenever you need to. Contacts and Calendar, unfortunately, do not have manual sync buttons (at least I haven't found them).
Battery hogs:
GPS
3G
Bluetooth
WiFi
Auto-sync
Screen brightness/duration
Also, I turn my phone off once a day, usually when I'm eating or something. I leave it off for at least 5 minutes. I've noticed that when I turn the phone back on, I get some of my battery life back. Like it'll say it's at 15% but if I turn the phone off and leave it for 5-20 minutes, when I turn it back on the battery might be back up to 18%, 20%, or even 25%
This is also a good way to clear out all those apps working in the background.
After all this, I'm usually able to go from 5am to 10pm without having to charge my phone. When I plug it in at bedtime, it's usually in the yellow, sometimes in the red. Since I sit in front of a computer for 8 hours a day, I do most of my surfing there, and I rarely get more than one phonecall a day.
There's also a battery monitor app that just got added to the market the other day, haven't used it, but it could be something else you want.