"Is Haskell as good as it gets?"It's debatable just how good Haskell and similar languages are. Like any language, it has its ardent fans and bitter detractors.
As for development of "advanced programming languages" in general, if you are interested in what's out there, I strongly recommend you browse the archives of the "Lambda the Ultimate" weblog:
http://lambda-the-ultimate.org/
There are a lot of very knowledgeable language designers on there, and news of advanced language features and new languages filters through there all the time. The blog is not as active as it once was, but the archives are still very much worth studying.
Another great resource is the old c2 wiki. Here are some relevant starting points:
http://c2.com/cgi/wiki?search=haskell
http://c2.com/cgi/wiki?search=lisp
http://c2.com/cgi/wiki?search=scheme
Finally, just hang around HN for a while, and you'll see plenty of posts discussing new "advanced" languages. The HN archives are also worth browsing through.