Once you have your iPhone up and running, ready to install new applications onto, what do you need? I'm talking about applications on your iPhone, not ones that are basically just websites.
Using the Nullriver AppTapp Installer, you have easy access to all these free apps (once you've installed the Community Sources and BSD Subsystem, that is) :-
For NZ users, start with the selection from Kiwi-ise. Add CallerID, Carrier Logo, Keyboard and perhaps Map Icon. You'll need a reboot, and a couple of changes in Settings, General, Keyboard to select only the NZ variant.
To help sort out settings and organise the desktop (SpringBoard) install BossPrefs and Poof. FTi will help you find the interesting Field Test application that's normally invisible. Don't forget to hold down any icon on the desktop to trigger the standard customisation mode.
If you want to get to the commandline, you'll benefit from both Term-vt100 and OpenSSH. You'll need the BSD Subsystem and SUID Lib fix to get the most from these (under 1.1.3, without SUID Lib fix, Term-vt100 cannot log in).
BossTool will help move things from the 300MB root partition into the ≈ 16GB /var. Fonts represented 84MB, Ringtones by default was only a couple of MB, and Applications was negligable (with only the apps named above being installed, that is). However, this has set up a symlink so future installs will go to /var anyway.
Sketches is a good diagram program. Not as good as Windows Mobile's Note program – it doesn't do text, but at least it's free-form drawing. RainbowLight is a great “torch” application, that will flash as well (shake the phone).
Converter has some great interface controls, MACalc provides an RPN scientific calculator, and LocateMe does a creditable job of providing Lat/Long from cell towers … and then linking you to the Google Maps app.
BallFight shows off the touch screen very well, as does Pool. ContraSense is a good-enough demo of the accelerometer control, but Labyrinth is better (despite only 10 demo levels).
FiveDice is a straightforward Yahtzee version. iGo is a front-end to GNU Go. Backgammon plays nicely.
Now I either need a toolchain to build native apps, or some time to look at Jiggy, which promises to run JavaScript applications …