I'll say it again: display is BY FAR the #1 opportunity for battery life - most other options involve a shift in usage patterns, which is what we all try to avoid doing. Get used to operating on min brightness indoors. If battery life is an issue for you, then also get used to letting the phone sleep after 30-60 seconds of inactivity.
Voice calls on the handset turn the display off. However, if you use a bluetooth or the speaker, I don't believe the screen turns off, so do it manually if you have no use to be looking at your phone while on a call. Same concept, turn off the display when using to listen to music and doing nothing else.
The other major thing you can do is root, because underclocking offers tremendous battery savings (especially when idle). But you have to experiment with different roms and kernels because in my experience battery usage can vary widely among different rom/kernel combos (talking like 10-20%).
Also, I'd agree axing the task killers can provide noticeable improvement in battery life. Oh, and it's better to use wifi vs. 3G when actively browsing or downloading, but turn it off when not in use (not a huge gain, but you might get another 30 minutes of active use).
Even widgets and programs like news apps that update frequently seem to offer very marginal gains individually, even in total I don't think the gain makes the effort and inconvenience worthwhile. But you could have a rogue app that was coded poorly burning battery, and the best solution is just delete the app.
