Get the BP7X battery from Motorola for $50. Be aware it makes the back of your phone thicker, and comes with a replacement battery door that only comes in grey.. If you have a case, you may have to remove the battery door to get a proper fit; This works perfectly with my Seidio Innocase. My battery is good for 2-3 days with light use, or a full (10hr) day of MP3s and some light web surfing will leave me with 10-20% when I get in my car. Also, stop using a task killer. If you're using it to kill all the stock bloatware, that stuff starts right back up in a minute, and takes MORE battery every time it restarts. Get Autokiller. It automatically kills empty/unused/background processes when your free memory reaches certain user defined levels. I have mine set to aggressive, and my free RAM almost never drops below 200MB. For example, when you quit a game, it stays in the background. It's ok for Autokiller to kill this, because it won't restart until the next time you click it. Also, get SetCPU, it allows you to set your minimum and maximum CPU speed on predefined profiles. I've got mine set to 300min 600max when the screen is off, or when the battery temp exceeds 42C. Finally, get titanium backup. You can use it to freeze all the stock bloatware (kindle, amazon, blockbuster, etc etc) that comes on the phone. It essentially hides them from your system, so they can't run. This will make your phone run much quicker, and your battery life will be better. However, when an OTA update comes out, you can simply unfreeze them, and your phone is factory new, and your OTA update works (I just did this last week with the latest one). Oh, and I use QuickSettings (free) to turn off my wifi/gps/3g whenever I'm not using them, as well as manually set my screen brightness.
You could also look into flashing the Fusion ROM (just search for it, it's everywhere) to your phone, but I'm not doing that because there's no SBF (backup file) for our phone yet, so if you brick it (unlikely, but possible), you're essentially screwed until that's released. We can only hope it's soon.
Hope some of that helps.