Juice Defender is one option. It keeps 3g turned off most of the time when phone is not in use.
You can set it to turn on once 1 minute every 15.
So if you dont need immediate email notification, this should help you.

Everything else will work fine, like sms and calls.

 

I get around 30hrs with a 1500 battery , biggest thing is when I'm home and at work which probably accounts for 2/3rds of that time it's connected to wifi.
I notice if I use only 3g and never connect to wifi I only can get 18-20hrs of life. I run CM6 Nightlies with the stock CM6 kernal , Set CPU set to 998 and a profile to set it down to somewhere around 384max 245min when the screen is off.
I keep screen 100% all the time, wifi and mobile network are always on, and I use a lot of bluetooth music and regular headphones as this is my main music player. Plus normal phone and internet usage

Start by look at any programs that might be draining you or if you're in a bad signal area and the phone is struggling to keep3g it will really drain . Also if you use Turn by Turn Navigation , or stream music via Mobile Network a lot those are battery killers as well