It seems like the JVM platform has the widest range of tools for RDF work, such as Jena, Sesame, Pellet as well as many other tools like Hadoop, GATE, UIMA and Lucene that are useful in connection with semantic work.
I've got mixed feeling about Java as a language (a stint of C# made it really hard for me to be satisfied with Java), and I'm thinking about alternatives such as Scala, Groovy and Clojure. Have you tried semantic work with alternative languages? What do you think about (1) use of Java-native libraries, (2) wrappers that make these more fluent, or (3) toolsets that are fundamentally based in alternative languages?
In my opinion, Groovy is a great DSL for Semantic Web programming. The metaprogramming features, GroovySQL and support for Java allows one to leverage the best of all worlds. Also, the Grails framework, with version 2.0, will give a good set of API's to integrate Semantic Web aspects into domain models and persistence mechanisms