When people I know switch to a Mac, I send them an email with a bunch of software I recomend to get up and running fast. Here is the list:
Internet Apps:
Adium: Best instant messenger out there.
NetNewsWire: RSS Reader
MarEdit 2: Blogging client…sort of like Mail, but for blogposts.
Transmission: Torrent Client.
Firefox 3 beta 3: Alternative browser to Safari(this beta makes it a good Mac citizen).
1Password: Password manger. Really helpful and it even supports the iPhone.
Cabo: P2P client that connects to the Gnutella network(like limewire).
Skype: Cheap VoIP calling and free video conferencing and chat.
Twitterific: Beautifull Twitter client from the Icon Factory.
Fluidapp: Make web apps, desktop ones
Skitch: fast screenshot/note sharing
Quicktime Video Codex:
Windows Media plugin for Quicktime
Perian: Plug in for Quicktime that adds a lot of video formats(divx, avi, etc).
Utilities:
Handbrake: My favorite DVD ripper.
Delicious Library: Organize all your movies, books, games in one cool program.
Awaken: iTunes connected alarm clock.
Acorn: Easy to use image editing software.
VoodooPad: personal desktop wiki.
Senuti: iPod music extractor
AppCleaner: Application uninstaller
Disco: CD/DVD burning with style.
The Unarchiver: Unziping .rar files(found sometimes in torrents).
Bootable backups (faster restore than Time Machine):
Developer Tools:
Coda: All in one web dev. No more cluttered desktop.
TextMate: The swiss army knife of text editors.
Cyberduck: Open Source FTP client.