Essential Mac Programs

I've deliberately kept the following list as short as possible only mentioning software that I find really useful. Let me know if I missed anything.

Included with Mac OS X

A lot of software already comes packaged with it, just check for it via the shell.

Fink is a SuSE Yast like package manager that gives you even more unix software.

OpenOffice: Completely obviates the need for any Microsoft Office software. The Mac version has come a long way. In fact so far, that I now prefer it to the slightly more Mac-compatible NeoOffice.

Audacity: Not the greatest of all user interfaces, but suffices for simple audio editing tasks.
Audio Recorder: If all you want is record audio from the mic.

VLC: Plays many movie formats (divx, avi etc.), including some that QuickTime cannot handle.
Handbrake: Great program for transcoding movies (e.g. from VOB to AVI).

New: Now transcodes many movie formats (and not just DVDs). This is great for converting movies to be watched on an iPod or iPhone.

The Gimp: The well-known open source graphics program.
OmniGraffle [commercial]: Indispensible program for drawing all kinds of diagrams, not too expensive!
GraphViz: The Mac version is awesome!
Skim: PDF viewer and annotater. Apple Preview has worked really well for annotating PDFs since 10.5 Leopard. But Skim is still indispensable for LaTeX editing, because it watches PDF files and auto-updates their display if they change.

SeaMonkey: The old all-in-one Mozilla internet suite. Only interesting, because it still has a good HTML WYSIWYG editor.
TextWrangler: Great text editor, free (light) version of the classic BBedit.
Aquamacs: Great for LaTeX editing (for which this Mac version has extra customizations).

Remote Buddy [shareware]: I don't like FrontRow completely taking over my computer. Thus, Remote Buddy is like FrontRow, but with normal Mac applications. An on-screen menu lets one change many settings with the Apple Remote.
Alarm Clock 2: Turn your Mac into an alarm clock. Works very well, because it also can wake the Mac up for an alarm. Furthermore, it can play any iTunes song or playlist of your choice instead of a simple beep.
nova media phone plugins: With 10.4 Tiger I could send text messages from my Mac via my old K700i Sony Ericsson. With 10.5 Leopard, this functionality was gone. Thankfully, the nova media phone plugins bring it back.

Unison: Brilliant program for synchronizing the files between two accounts. I use it to keep my (Linux-based) account at work in sync with my iMac at home.
The Unarchiver: Decompresses many more file formats than the standard Apple unpacker.
BusySync [commercial]: Keeps iCal and Google Calendar in sync. Also lets you share iCal calendars on a LAN, but I've never used this functionality.

Google Calendard CalDAV support: Might be a free alternative to BusySync. Not tested, yet.

Displaying the Dock in the upper right corner (as opposed to centered on the right)
Completely hiding everything on the Desktop (when recording screencasts)

TODO:

The following programs look interesting, but I haven't yet had the need the try them out.

Tinderbox: Note management, a combination of mindmapper, small database, outliner.
Evernote: Versatile note-taking application that synchronizes with an online account and/or mobile devices.

Vector graphics: OmniGraffle currently fulfills all my needs. But there are some interesting and relatively cheap vector graphics applications out there: