I've added a derived major mode for ClojureScript. It's derived from the clojure-mode. It's a good start on providing first class support for ClojureScript in emacs.
The main thing that it provides is support for the ClojureScript REPL through inferior-lisp. Someday it might be slime, however I'd really not go into rewriting the swank protocol right now. For information how how REPLs work, checkout the wiki page. ClojureScript provides a REPL through it's own REPL interface with evaluation implementations for Rhino and a browser.
I've been using it against the browser environment and it's been working great.
added derived clojurescript-mode with REPL integration
+1. I have my own little hack for this and it would be great for this to just be a part of clojure-mode.
Thanks. I tidied it up a bit, adding autoloads and explicit checking for the necessary environment variables. Feel free to upload to marmalade.