HTC Desire & HTC Dream(Basically using the same apss):

AppBrainMarketSync(http://www.appbrain.com/)(Browse apps on your computer and then choose the one you want, sync it to your phone and walah!)
BatteryTimeLite
Dolphin Browser(something like firefox)
chompSMS(prefer this more than handcent)
FxCamera
aCurrency
ASTRO
Meridian player(music,video player)
Advanced Task Manager
silentMode(widget)
AK Notepad
Tech Buzz(news widget)
Gaming Buzz(news widget)
Engadget(news widget)
3G watchdog(widget)
JuiceDefender
SD Card Memory Widget
& Many more...

The ones i listed are basically i use most of the time...

Those who are able to purchase apps...
What paid app is a must? wanted to try some paid apps but none really interest me..

lol.. i can buy ma cause not in m'sia =P