See the Language Specification in a RoboHelp (WebHelp) version or Flash Help version, both with excellent full-text search.
ditamap.com has a frameset view of the language specification.
gotAPI.com has an excellent frameset view with progressive search.
DITA 1.1 is now under review. The DITA Version 1.1 release consists of an architectural specification, a language specification, a set of DTDs, and an equivalent set of Schemas. All interested parties are invited by OASIS to participate in this review.