Been reading up a bit lately on Haskell and observing that there are a ton of monad tutorials out there. I’ve looked at a few and I have to say that my current favorite is:

A Neighborhood of Infinity: You Could Have Invented Monads! 

mostly I think because it’s interactive and guides you to discover the concept instead of spoon-feeding it to you. I recommend firing up GHC and trying the exercises he gives you.