On: Monads as a Programming Pattern

[hardwaresofton]

Another really good functional (as in related to how they work) explanation of monads:

http://adit.io/posts/2013-04-17-functors,_applicatives,_and_...

It's somewhat more than a monad explanation -- it covers functors and applicatives, and is somewhat haskell specific, but it was one of the guides that really clicked for me when I was trying to grok monads