In my recent quests to find a replacement for Python, I've found a few languages that look very appealing. Io is one I'm playing with and another I'm taking a long look at is Scala. Scala, while not quite as fascinating as Io, is probably a lot more practical for doing "real work". It runs on the JVM and can access Java libraries, there's at least two usable web frameworks for it (sweet and lift), and performance-wise it's not as fast as Java, but much faster than your typical dynamic language.

Scala is interesting in that it's strongly typed (and can accept static type declarations), but they aren't strictly required (it seems to do type inference). It also supports the actor-model of concurrency, anonymous blocks and functional programming.