Latest Atom Spec
The latest draft version (05) of the Atom format specification is out, and it has really shown an amazing amount of improvement since the 03 version. The document itself is very well organized, with the welcome addition of Relax NG fragments throughout the document. Makes it much more readable.
We're staying on top of this at FeedBurner, so hopefully we can support the revised spec right after it is approved.
Source: The Atom Syndication Format