Well, I'm currently learning Haskell, and http://learnyouahaskell.com seems to be pretty good.

This site is also the inspiration behind http://learnyousomeerlang.com/

LYAH is good for basics, but you won't be able to use modern Haskell libraries, there's a lot more to Haskell than what's in there (monad transformers, etc.)
And it doesn't encourage practicing, which is pretty much the only way to "get" Haskell (apart from learning category theory, check out Bartosz Milewski's videos on YouTube if you want an understandable introduction to category theory, he's really good).

Allow me to recommend this after (or instead of) LYAH: https://github.com/bitemyapp/...

@MrJimmy
See this: http://stephendiehl.com/posts/...

Apart from being a research topic, Haskell is a general purpose programming language, so at the very least it can do whatever any other general purpose language can do.
That said, Haskell has a few advantages over other languages, like easier expression of certain types of ideas (combinators, functional reactive programming, parallelization, etc), safety (because of how strict the language is about types, immutability, etc), and so on. As far as I know it's used for data access in Facebook (Haxl), data analytics, spam filtering, etc. It's not really a thing if you want low latency code, Haskell seems to be more suited to making data processing pipelines (though well written Haskell produces pretty fast code).
I find Haskell a hell lot easier to test, debug, and maintain too (compared to C++/C#/JS).
Plus, you have goodies like lenses and other TemplateHaskell trickery.