Essential iPhone apps

So now that I've joined the collective, I was wondering what those of you who have this device consider essential applications.  Currently, I have the following that I've found to be useful:

Pandora
Google (enhanced search client)
Google Earth
m-Box Mail (native Hotmail client)
LiveJournal (native LJ client)
Yelp

Are there any others that any of you consider essential and/or useful?