Uh... simple solution: Airplane Mode. Download the app Airplane Mode Toggle. Put the phone into airplane mode when you are not using it. This turns off the radio (and 3G) and Wifi. It also stops all apps from trying to do things in the background.
What kills your batter is not the fact that the radio is on, it's the fact that a bunch of apps are *constantly* trying to send and receive data. This consumes battery. Turning off the radio (3G, with airplane mode) stops this. I guarantee that you will greatly extend battery life doing this.
If you simply don't ever want to turn off the radio then you are SOL.
Also, turn off all apps and check running apps in settings. You probably have apps running that you don't even know about, and that shouldn't be running. Lots of widget apps, keyboard apps, things like that are killing batteries. Uninstall them and go with stock widgets and keyboards. Also, uninstall task killers (they don't work, Android simply turns back on whatever it thinks it needs) and antivirus apps (as there is pretty much no virus threat on Android).
Do all of this and your battery life will be greatly extended.