Here is a quick list of the current CSS specs and drafts. See CSS Snapshot 2007 for some extra information. These are in various stages of completion.
The current CSS standard is CSS Level 2, defined in CSS 2.1 Specification. This supercedes the previous Level 2 spec and the long-gone Level 1 spec.
This approach, of having supplementary specifications for niche requirements, seems to have been adopted to allow an incremental definition of CSS 3. So there are various specifications or drafts such as: CSS 3 Model: Paged Media, CSS 3 Module: Fonts, Selectors, CSS 3 Module: Web Fonts, CSS Color Module Level 3, CSS Marquee Module Level 3, CSS Basic Input Module, CSS3 Ruby.
To see where CSS3 is going, and to find links to the multiple other specifications, many of which seem to be bumming around in Working Draft status, the place to start is the roadmap Introduction to CSS3. However, this document was written in 2001, so it could well have out-of-date parts. On the W3C website, there are CSS drafts for backgrounds and borders, grid positioning, basic box model, advanced layout, multi-column layout, generated content for paged media, text, values and units, cascading and inheritance, speech, hypertext presentation, presentation levels, syntax, borders, lists, and line formatting.
RelatedThese don't nearly exhaust the universe of formatting possibilities. For example, there are several other East Asian formatting idioms that are not present. The W3C's excellent Internationalisation Working Group has a draft Requirements of Japanese Text Layout which is also applicable to Chinese and Korean layout, with the details adjusted. Some issues related to right-to-left scripts can be found at Internationalization Best Practices: Handling Right-to-left Scripts in XHTML and HTML Content and some general requirements for internationalization can be found in Internationalization and Localization Markup Requirements.
And, of course not to forget the format objects in DSSSL Online (not W3C page): a profile/subset of ISO DSSSL that informed XSL-FO. And for XSL-FO, see Extensible Stylesheet Language (XSL) Version 1.1