Useful guide from PC World:

For many users, getting started with Linux is surprisingly easy. New, friendlier versions of the free operating system, such as Fedora and Ubuntu, feature straightforward menus and automated installations that make switching from Windows to Linux a relatively simple process.

But a lot of people who try Linux dump it and switch back to Windows the instant they want to get some work done, mostly because they don't know which Linux programs to use in lieu of their old Windows standbys. Fortunately, such confusion need last only a moment.

Linux offers equivalents to many Windows applications that are often as good as--or even better than--the programs you're used to. In some cases the apps are also available in Windows and Mac OS versions, allowing dual-booters to stay with the same set of free programs regardless of the operating system in use.

Office/Productivity Programs

Web/Internet Apps

Audio/Video Playback and Authoring

Other Apps and Utilities