Also known as a short recap of useful info prior to recklessly upgrading my iPhone to the 3.0 OS.

Most of these applications are free or are in a ‘lite’ edition, although some may be obtainable only through the Cydia distribution system, which requires the jailbreaking you iPhone (or iPod touch).

To-do list apps:
iDoLite
WhatTasks
TodoList
SimpleToDo
myTo-Dos
DoBot ToDos
To Do
TooDoo
HPlanner (for education)
Divide Lite
EasyTask
To Do’s

GTD-oriented to-do list apps:
Simplist
Action Lists Lite
Nozbe (needs an account on www.nozbe.com )

Calendaring apps:
Calendar (Apple’s MobileCalendar)

e-mail apps:
Mail (Apple’s MobileMail)

Bonus:

Time tracking apps:
Time Tracker Lite
TimeSheet