I'm a big Erlang fan. Its not "pure" functional. That's by design and although the syntax may seem foreign at first, its easy to learn and was designed to be easy to teach "telecom engineers" who weren't traditionally trained CompSci folk. Erlang has several decent WebApp Frameworks. I like ChicagoBoss.org as an easy start.

Erlang is more than a functional lang. It has concepts of concurrency and "let-it-fail" which helped to change my view on how to write server apps.