Choose from a very wide range of software in certain application areas. For instance, the range of text editors and HTML editors is larger than in other systems. I’m comparing the free Linux applications to the non-free Windows applications. If you count only free applications on both systems, the difference is even greater.
Most (many?) major programming languages are available on Linux, at no cost. These versions of the programming languages are either similar to or superior to the versions found on other systems, for the most part, as far as I can tell. (There will be exceptions, and I’ll let the trolls point them out).
A lot of the standard software that people have heard of, such as the applications that come with Microsoft Office, have “equivalents” in Linux. They are not exactly the same, though. The Linux apps are generally better. They load faster, they are more reliable, they read and write to a wider range of formats, they are less annoying, generally better designed. Plus, you can run most or all of the Microsoft Office applications on a Linux computer (this may not apply to the most recent versions of Office … that depends on when you read this!).
There are a number of cool Linux applications that you only have available on Linux, that are in my view far superior to any other similar software on any other system, and are free and run more reliably. Two examples are Gnumeric, a spreadsheet, and Xara Xtreme, an excellent vector based drawing package.