| | Moving beyond Microsoft
I left MS for Linux some time ago and recently purchased a Mac. For those who are interested in making the Mac plunge:
Quicksilver - ultimate app launcher and productivity tool. (Mentioned above)
TextMate - well-featured text editor and development environment. You can edit text files, post to your blog and program in any of a host of different languages. (unlike the rest of the list, this costs money)
I use Thunderbird and Firefox for email and browsing, but the Mac-default Mail.app and Safari are both highly capable
Aurora - iTunes-linked alarm clock with tons of cool options
NeoOffice - Free, Mac version of OpenOffice. Handles .doc, .xls files from MS Office.
VLC - universal media player
Kinkless GTD - a well-supported GTD setup for Mac. I actually wrote my own GTD app that's highly customized to my needs (I'm a software developer), but I've tried Kinkless and it seems quite capable.
Google apps - All of the Google stuff (Gmail, News Reader, Spreadsheets, Docs, etc) is of course still available on a Mac. Their stuff is handy since you can even use it from someone else's computer in a pinch.
I've found the Mac to be a well-engineered machine. I'm able to run Linux programs with the included X11 support, and I have a suitable command line for advanced tweaks, yet the overall user experience is very polished and accessible for beginners. The folks at Apple really understand user-oriented design.