Doc continues to be a challenge, but there's a lot of good stuff at http://docs.scala-lang.org/ including an in-depth guide to collections that the author might find helpful.
In general I think a site for language docs where people can add comments/examples/content would be extremely useful. Like the php docs but for all languages in the same place. I never use php but comment-able docs are a win.
APIdock (http://apidock.com/) already has the “commentable multi-project documentation” infrastructure in place, though it only has the Ruby language and two Ruby libraries on it right now.
For beginners http://dcsobral.blogspot.com/2011/12/using-scala-api-documen... may be helpful in learning how to navigate the docs buuut what really helps are examples especially with scala's sometimes long and hard to parse type signatures.
In general I think a site for language docs where people can add comments/examples/content would be extremely useful. Like the php docs but for all languages in the same place. I never use php but comment-able docs are a win.