I’m an Apple computer user since 1984 so I was very pleased when a very Cultivated and High talented mindset information system senior Architect, who I’m Proud to be counted as one of his friends, has decided to switch on September. I often told him instead of struggling every week with is PC on bugs, he should invest in a MAC for many obvious reasons. Congrats!!
Some discussions we had on that, gave me the idea to post what are my selection on MAC OS X.!
What is yours ?
Browsing: Mozilla Firefox by default. Shiira 2 or Sunrise are very good too.
Safari 3 is good. However, the plugins available for Firefox allow a better web navigation experience.
Shiira is a also very good alternative to Safari and sometimes to Firefox. Some interfaces features are very usefull such as a real fullscreen mode (like Coverflow in fullscreen) or PageDock. It proposes a new way to navigate within the tabs using a dedicated bar of snapshots/preview on the bottom of the browser.
RSS Reader: NetNewsWire. A good alternative is Vienna. (sometmes faster & more effective than NetNewswire)
Email: Mozilla Thunderbird (with Mozilla Lightning= Mozilla Sunbird plug-in)
Multi-OS with same features and behavior. Unfortunately, no Xobni yet!!
FTP: CyberDuck and/or FireFTP, a plugin for Firefox.
Brainstorming: XMind
Productivity: iWork for $79 (cheap compared to Mac Office 2008), however it’s worth it. The 3 tools, Pages, Numbers & Keynote, are very easy to use and powerful.
The free alternative is OpenOffice.org 3, although it’s still in beta version. Abiword if you’re only looking for a word procesing tool.
Online Productivity: Zoho and SlideRocket for awesome presentations available from anywhere
Text Editing: Smultron , Bean, TextWrangler
Media Player: VideoLAN
Imaging/Picture: Skitch. I use sometines also Inkscape, Seashore and Picnik,
3D creation: Blender
Notepad/Post It: Evernote
Micro-Blogging: twhirl
VPN client: Viscosity
P2P: Transmission
WiFi: coconutWiFi
Better tool than standard airport one to manage wireless connexion and get info on hotspot.
Uninstaller: AppCleaner.
Backup: Mathusalem (associated to Time Machine), iBackup
System Utilities: Onyx (or Deeper for less customization options), coconutBattery, DeployStudio (a very good system backup),
Automation: Quicksilver a hi-level very nice & powerful app launcher,
HDD scan utility: GrandPerspective
Burning CD & DVD: SimplyBurns
IM: Adium multiprotocols (14 in fact) on a same very nice & powerful GUI.
VoIP: Skype
because even iChat is much better for video conversation, it’s only on Mac OS X. There are still more MS windows users than feline OS ones to discuss with.
Astronomy: Stellarium
Sport: TrailRunner. A must to have if you like runnng, hiking or biking.
Games: Battle for Wesnoth (Strategy), Quinn (Tetris-Like), Fexaze (puissance 4 like), Solitaire XL
Raym.Blog 
My 2 cents:
Automation: Quicksilver, TextExpander
Screencast: Screenflow
Text: TextMate, TextWrangler
Imaging: Skitch, CandyBar (Icons), Pandora
RSS Reader: NetNewsWire
Email: MailPlane
Notepad/Post It: Evernote
Micro-Blogging: Tweetdeck
FTP: ForkLift
Disk Management: DiskInventoryX
Thanks for your list DidierB.
A quick remark on your selection, most of the tools are not free and/or opensource.
MaiPlane is fantastic. However, if you have others accounts with different providers such as yahoo or free (for french fellows), MailPlane is only for Gmail account and not free (cheap but still $24.95) except if you’re using the MaiPlane v2 Beta.
All the Panic solutions are very awesome such as CandyBar you mentioned and I will add Coda and Unison.
I forgot the Imaging/Photo/screencast tools in my list. I will fix that. Effectively, Skitch from Plasq is very powerfull and easy to use if you want to create an illustration. For pictures management and enhancement, Flickr+Picnik or Flickr+Photoshop Express are both complete tools as alternative solution if you have a web access available wherever you are. Screenflow is the best tool currently available on Mac.