My use patterns are as follows:

Everyday:
Touchdown (for Exchange)
Dolphin Browser (now my default for most tasks)
Droidbox (different app to access Dropbox)
Weather Widgets (current/forecast weather display right on desktop)
ContactOwner (runs in background, so technically always on, but not so essential.. until you misplace your eDGe)

Occasionally needed:
AndroidVNC (for remote desktop connections)
Google Voice mobile (for call connect callback service - voice does not work)
Radiotime (might turn into everyday when I get my bluetooth headset)
Better Term Emulator Pro (for geekier stuff)
Taskkiller (kill kill kill)
ES File Explorer (comes with latest update)
Docs 2 Go (preinstalled)
Note Everything (use mainly for drawings on LCD side)
SAM SlideMe app store


Newly installed and looks promising:
Fring
PrinterShare
Pandora