I am a big fan of "using the right tool for the right job".
Although I usually use Java (for mostly server side development), I use both Common Lisp and Smalltalk for experimenting with new AI NLP algorithms, etc. - these langauges and programming environments just let me get a lot of work done quickly.
The ultimate high programmer productivity programming language (for some programming tasks) is Prolog. The link for this article is for a very high quality, free, LGPL licensed Prolog system that works well embedded in C/C++ applications, interactive experimentation, or turnkey pure-Prolog applications: Swi-Prolog.
I started thinking more about Prolog yesterday when I posted to Slashdot (on Japan's new multi-year build a super smart robot project). Japan's 5th generation project was based on Prolog-like languages.
Getting back to Swi-Prolog: there are many included packages for both client and server web based applications, etc. My current favorite package is a library to manage RDF - stuff for the Semantic Web.