Advanced task killer a must. I also used to use iMusic for songs, but it doesnt seem to work anymore. I found a new one called Gtunes you can get it right from the Android market. I also use colorflash for a flashlight, just turns your screen white and its bright, you can also change the colors and do other cool things like strobe or police sirens or even a candle! Another good one is WiFi On/Off it is simply a widget you put on your home screen to turn your wifi on and off without going through the whole menu. So to make it easier here is a small list of the above:
Advanced Task Killer - Saves battery by ending running apps in background
Gtunes - Music
Color Flash - Flash light app
WiFi On/Off - Turns wifi on/off without going through menu (the one I use is by curve fish, search "wifi onoff")