There are many languages out there with interesting type systems.

• Nice - The Nice programming language. Runs on a JVM, much more interesting type system.
• Haskell - Scary functional programming malarky. Not terrifying me as much as it did 5 years ago at university, though. Will keep reading. UPDATE: Have now ordered Haskell: The Craft of Functional Programming. I won't have time to read it, but when has that ever stopped me buying books?

I will probably babble further about these in the future if I get the time to read more.