iTunes
Easily one of the greatest media players available today, iTunes offers music, movies, and a music store, all blended together. Make a playlist, add songs to your iPod, watch a new movie that just released. iTunes is a fantastic experience for any Mac (or PC) user. And guess what? It’s waiting for you at the bottom of your screen. (Mac only :D)
Mozilla Firefox
The Browser That Has It All: Firefox has security, speed and new features that will change the way you use the Web. Don’t settle for anything less.
Adium
Adium is an awesome Multi-Client Instant messaging service for Mac OS X. The user interface is neat and simple, and it works great! Very easy to add ALL of your Instant Messaging accounts to one easy-to-use environment!
VLC
Goes with Flip4Mac and is a good player for non-mac media codecs
Perian
Perian is a free, open source QuickTime component that adds native support for many popular video formats. Good replacement for VLC.
Quick Silver
QuickSilver is “A Unified, Extensible interface for working with appliations, contacts, music and other data” and completely free.
smcFanControl
smcFanControl lets you control your fans manually to make your MacBook(pro) or Mac mini run cooler.
Flip4Mac
Got a weird video from your Windows friends? Well this will allow you to play virtually any video codec!
Transmission
Transmission has been built from the ground up to be a lightweight, yet powerful BitTorrent client. Its simple, intuitive interface is designed to integrate tightly with whatever computing environment you choose to use. Transmission strikes a balance between providing useful functionality without feature bloat. Furthermore, it is free for anyone to use or modify.
DropBox
A sleek file syncing program. Multi-platform syncing with a web interface for access everywhere.
If you have any other suggestion of things that are missing or in the wrong place please start a discussion by commenting below.
This list was pulled from apple.lockergnome.com on 7-17-08 and I take no credit for it.