Here's my short list:
Advanced Task Manager
Amazon Kindle - book reader
Angry Birds - you should know by now what this is
Barcode Scanner - Scans barcode and IDs the product - awesome with the new camera kernel
and FRX05
Chase - used for my checking account; I've deposited checks using the camera
Dophin Browser Mini - alternative to the default browser, fast, flash capable but slow
DropBox - file repository using for sharing between your PCs and devices
No Lock - I can't stand the builtin slider lock so I use this to disable it
Pandora - Music streaming
Quick Settings - quick access to most used setting controls
Quote Pro - Stock quote streaming
Root Explorer - file manager
ESPN Score Center
SetCPU - Overclocking app
SlideIT - like swype but better
SlingPlayer - watch TV from your SlingBox
TapaTalk Pro - Forum reader/posting