Welcome to the wonderful world of modern smartphones - unfortunately, despite annoucements every other week, battery technology has singularly failed to keep pace with power demands of modern gadgets.
There are, however a number of things you can do to reduce the load on your battery which might eke out a little more time for you:
- reduce screen brightness
- minimise the screen time-out
- turn off sync
- turn off radios you're not using (WiFi, GPS, Bluetooth)
- turn off 3G in areas with poor reception
You should also check your battery stats (in Settings .. Battery) to see if you have any rogue apps that are eating battery.
Most of these suggestions will make a marginal difference at best though so don't expect a huge improvement
If all else failed, you could get an external battery pack or a separate battery if your phone has a removable battery.