You can make massive differences to the battery life by turning off a lot of the things that are autosyncing - like Facebook, Twitter, the Weather, mail etc. I mean I don't need to be insta-notified every time some t*** sends me a spam email so I have all that auto stuff turned off, and just refresh when I want to check my mail.
Try Y5 as well - turns off wireless when you aren't in range of a known wireless network (i.e. one you've connected to previously). And when the update to 2.2 hits (coming soon), you'll be able to save apps to the SD card.