I've just seen an article up on Cnet - assuming you can call it an article.
Windows Future Store, or WinFS, a file structure that would allow for database like searching on your desktop. You could organize files by context, location, or metadata, greatly simplifying information storage and retrieval. WinFS would basically abstract your information; you wouldn't need to worry about where it was literally stored, since you could just search for anything, anywhere on your hard drive, and have it pop up in a single results pane.
Avalon, the presentation and graphics infrastructure, including the new XAML programming model for application UI design.
Indigo, the collection of .Net technologies that serves as a communications platform for applications and Web services.
Here's what you'll be getting.
No WinFS--not for the desktop, not for the server.
Indigo and Avalon have been uncoupled from Longhorn, meaning they'll be made available as, essentially, plug-ins to Windows XP when and if they're completed.
Right let's address a few things. The first "fact" of the article is wrong, WinFS isn't that at all. Longhorn will still allow all of the above "WinFS" features Molly mentioned.
Indigo and Avalon will be shipping for Windows XP also, this was due to pressure from developers wanting the maximum user base for their applications. It's still included in Longhorn.