My Dell laptop finally died.  A month short of five years.  So I bought a 20" iMac, loaded.  What are each of your "won't live withouts" for a mac?

I got parallels and set aside some money for when Leopard comes out, too.  I was trying to hold out until it was released.  Too bad.

Terminal.app and all the unix goodness
Adium
Textmate
quicksilver
aperture
virtuedesktops
the nice iterconnectedness of the various iapps
parallels can be useful now and then
emacs keybindings and spell checking in almost all text entry fields (assuming it is a cocoa based app)
xcode and interface builder and nice ways to try to build GUI apps, too bad none of the apps I developed can be targeted that way
i am sure there are more, but I can't bother to think about more things right now, over all I find the whole deal just works the way I want to

I think I echo most of what stuka said

I won't live without:
TextMate (soooo good)
LaunchBar (instead of Quicksliver; apparently I'm behind the curve on this one)
Terminal.app
Safari
Firefox (since web devs actually target it these days)
Mail.app
iTunes
iCal
X11/gnucash (via...)
fink (instead of Darwin Ports; I think I'm behind the curve here again)
Pages (I use it every chance I get, though it takes some getting used to)
OmniOutliner
Preview.app

Also quite useful:
LaTeXit (creates LaTeX snippets you can drop into Word, Pages, etc.... good bye Equation Editor)
HandBrake (rips DVDs)
Remote Desktop client
CocoaMySQL
Excel
OmniGraffle
sshfs via MacFuse

Also, it looks like apache is being a little stupid.  If you have trouble using preview or post, switch over to port 8181.

Thanks, both of those posts were really helpful.  Especially the DVD ripping recommendation, which is always an App I have a hard time deciding on.  It should be here in a few days - I'll let you know what goodness it brings with it.

preview, handbrake and the omni apps

I have also started to look into some other strange apps: yojimbo - note store catch all and voodoopad - desktop wiki style program

Stickies
lyx
SubEthaEdit (Perhaps I should check out this textmate device?)
ipodrip
omnigraffle
Reunion (yeah, geneaology!)
Also, external drives are crucial - I think they have for the mac minis some manner of one button back-up device - if that is an option available to you, I would go for it.
Also, disk utility is pretty handy.

It is not so much an app, but it is a great bit of the X, also the great drag-n-drop support everywhere

Everything worked flawlessly, as expected.  Needed a mini-dvi to dvi adapter, which I lived without for a day.  Dashboard and hot-corners or whatever are my favorite (since I can't get F9-F12 straight, I just put one in each corner).  Vista sidebar will never live up - real estate is too limited without overlay.  The gadets are cramped and worthless.  So it's nice to be able to do my dev work or a remote desktop session but still have Dashboard.  I keep using mac keyboard commands in Vista and vice-versa.  That shit needs to be standardized already.

I think not having a button to eject your combo drive is one of the dumbest design decisions Apple has bull-headedly persisted over the years.  I've already had it not eject properly a few times - I've been using iTunes or the shell.

Got Parallels running in composite mode with Vista and Office 2007.  Fast except for some of the redraw, which is due to parallel's crappy 3d graphics support in their driver, from what I've read.  I laughed that Parallels set up Vista and launched you right into the Admin account for use.  Mac/*nix people would be furious at such a blatant misuse of elevated privelage...haven't heard a peep out of Windows folks.  I'm pretty sure they didn't notice.  Sigh.

Just need a USB hub and an external backup drive and it'll be magic.

I'm glad to hear things are running well.

The eject button on the keyboard is a bit of a mystery.  I'm not going to take sides on that one, but I will say that stuck disks have been very rare in my experience.

Fourtunately, i'll be joyning the intel-mac'd gentry soon.  I have won of them thar touchpads with built-in lightbox that runs on uh few D batteries coming in sune.