Windows XP is going to be king of the hill for quite a long time. The first beta of Longhorn, the next version of Windows, was originally slated for this Fall. But Microsoft has confirmed that Longhorn beta will show up in 2004 with the actual release sometime in 2005.
Longhorn comes with a host of new features such as a new display technology for much faster visual display (and hence able to provide much more complex effects), a new file system called WinFS, and a host of other enhancements.
In the mean time, Windows XP's popularity due to its reliability and ease of use have made it a hard act to follow.
You can read more on Paul Thurrott's WinInformant website.
