While PureScript looks very cool, if you're interested in solving callback hell without changing the whole language, StratifiedJS is a superscript of JS that adds straightforward sequential-style code which is async under the hood, with a bunch of concurrency constructs built into the language:

http://onilabs.com/stratifiedjs

(Also, not terribly relevant to the discussion, but the fact that almost every line is abruptly broken mid-word without any hyphenation makes the article rather jarring to read)