I have a pleasant decision to make: I am going to soon startup a long term consulting job and I have been given some flexibility in programming languages to use. I am fairly sure that I am going to use Ruby for all utilities for file handling, data conversion, etc. and use Common Lisp for the main AI component. I made a strong pitch for doing the web interface using Ruby on Rails, but my bit is the back end AI work, so I don't care too much what other people on the project use. I am still considering doing the AI part in Ruby also, but I am a little concerned about performance issues. I have also heard strong rumors that an awesome knowledge representation system PowerLoom that is available in Java, Lisp, and C++ might be open sourced. PowerLoom is a great framework - in the past I have only experimented with it because of its non-commercial license; if it is open sourced, I think that will change the landscape quite a bit for choosing frameworks for AI projects.