SML has been on the higher ranks of my to-learn stack, because apparently it has some nice features Haskell does not, most notably I've heard great things about the module system.
The first language is ML and than moves to Racket. Really learned a ton just doing the first weeks. It is more of a CS 202 Programming Languages course which was perfect for me since I really wanted to learn more about functional programming.
Edit. Oh, and here's a previous discussion: https://news.ycombinator.com/item?id=2433860
There are plenty of suggestions here http://www.smlnj.org/doc/literature.html