HTC Droid Eris

I easily get a full day out of mine. If I had better reception in my apartment, I could probably comfortably get two days of usage per charge. I'd recommend three things...

First off, make sure that you only enable wireless modes that you're using at any given time. The easiest way of doing this is to add widgets for each of the wireless settings that you'll use, thus allowing you to easily enable/disable them with a single press.

For example, you should only enable Bluetooth if you're using a Bluetooth device. Only enable GPS if you're using location-aware apps and services. Only enable Wi-Fi if you're near a usable Wi-Fi hotspot.

Secondly, use a task manager. I recommend Advanced Task Killer. Just use it to kill off any app that you don't need notifications from periodically. If you need to keep another task that you don't usually leave running, then simply uncheck it on the app list within ATK.

Lastly, change your sync settings to only have apps sync in appropriate intervals. For something like Facebook or Twitter, you might want it to update every hour or so, while you might want news feeds to only update every few hours. More synching equals poorer battery life.