Rich Internet Application Development Tools
I have been hearing more and more about Adobe AIR, Microsoft Silverlight, Mozilla Prism, Google Web Toolkit, etc for developing desktop-based Rich Internet Applications. These applications run outside the browser and leverage the desktop functionality to give the user a much better experience. Here is a good article with a brief description of the tools.

I think that Adobe Integrated Runtime and Silverlight have the most buzz. Also, from what I can read in the blogosphere, Adobe is ahead.