OK, you smart phone users, what's useful, fun, or just cool? Hook your fellow Heffas up.
Bonus point for free.
Two of my favorites so far:
Dragon Dictation - speak it then send it as an email or text or copy/paste it wherever you want. I was shocked at how well it worked out of the gate; no training sequence needed.
Evernote - Text, image, voice notes can be annotated, tagged and automatically synchronized to your desktop. There's a Firefox plug-in that lets you save stuff from websites kind of like Google Notebook.