Here's an (incomplete) list of the software and tools I prefer to use:

Internet Browsing
I use Firefox3 as my primary browser. Here are some of the extensions I have installed:
- Colorzilla - allows you to pick a color from a website
- Delicious Bookmarks - allows me to access, create, and search my bookmarks wherever I go
- DownloadHelper - allows you to download embedded flash. movies, objects, etc
- Firebug - the BEST tool for web development. GET IT NOW
- FireFTP - a FTP client that fits nicely into a tab in FireFox
- MeasureIt - allows you to measure distances on a website
- Web Developer - another essential tool for web development
- YSlow - a Yahoo! plugin used to evaluate and analyze page load times
I also use the following browsers for testing web apps: Safari, Flock, Camino, Opera, & ies4osx. IES4OSX allows you to install Internet Explorer on a MAC using Wine for OSX, sweet!

Development
I run OSX as my primary operating system. An operating system is useless to me if it doesn't have a fully functional shell. I use Parallels to install a Centos virtual machine (with no GUI). Centos is used to run LAMP and any other development and application services. I then connect to my linux filesystem using Samba and SSH. I use Eclipse as my primary IDE (with the PDT plugin for PHP). For database management I use Navicat and MySQL Tools. For a Subversion client I use Versions.

Other
- Quicksilver - file/application indexing to increase productivity
- Adobe Photoshop CS3 - image creation and manipulation
- Aquamacs Emacs - text editor
- FFMPEGX - video conversion
- Fugu - secure file copy
- Google Notifier - email and calendar event reminders
- IPSecuritas - VPN Connections
- Skype - Office chats, video conferencing, IMs
- iChat - IMs & video chats
- iTunes - I listen to music all day long off my iPod
- NeoOffice - OpenOffice for OSX (FREE equivalent of M$ Office)