I think the best intro is http://www.pragprog.com/titles/jaerlang/programming-erlang, which comes in PDF form but also costs $22.00. As far as free resources, there's http://erlang.org/doc/getting_started/part_frame.html , which isn't nearly as fun as _why's guide, but is informative. I personally just bought the book; it's really well written and actually got me interested in using the language.