My favourite language for the past several years has been Python due to its depth and its breadth. Lately I have recently worked with node.js and I am very impressed with its capabilities and flexibility. I use my own build of Python that is portable (to Linux OSes) and entirely self-contained.
Lately I've been coding an application and some tools that make use of AMQP messaging, in particular using RabbitMQ as the MQ Broker. I am very impressed at how AMQP, combined with network db APIs, lets you build an application in many small decoupled components that can easily be scaled on one or many servers.
Since RabbitMQ is implemented in Erlang, I learned enough Erlang to make a simple management app that runs on an independent Erlang node, i.e. not a RabbitMQ plugin. And since my company's main language is Java, I am now learning Scala (with Akka actors) since this JVM language has part of its heritage in Erlang.
Q&A for professional and enthusiast programmers
Q&A for professional system and network administrators
Q&A for computer enthusiasts and power users
Q&A for users of Linux, FreeBSD and other Un*x-like operating systems.
Q&A for professional programmers interested in conceptual questions about software development
Stack Exchange Network staging zone, where users come together to build new Q&A sites
Q&A for peer programmer code reviews
Q&A for members of the workforce navigating the professional setting
Q&A for meta-discussion of the Stack Exchange family of Q&A websites