My buddy David Pollak, host of a local geekbeer social event, thinks Scala is the next big thing in web programming. Scala is an object-oriented / functional programming language that compiles down to Java byte code. It's statically typed but fully supports generics and polymorphism. And it's published under an open source BSD-like license.
David's got pretty good street cred; he's built large scale applications in everything from C++, C#, Ruby and pretty much everything else in between. Over lunch recently he told me in a rather offhand fashion that he used Scala and the related lift framework to write a Twitter clone (called Skittr) in 800 lines that scales to 1 million users on a two-box Intel Core Duo setup. Holy cripes, that's scalable.
Part of the reason Scala's able to do so much with so little code comes down to the framework called lift which is also open source under an Apache license. Lift takes all that is good about the Rails framework for Ruby but performs 6x faster and is fully multi-threaded. It's still in an alpha stage, but looks pretty impressive.