I have experimented with Lisp (actually Scheme) and found it to be a very beautiful language that I am interested in learning more about. However, it appears that Lisp is n
ITA Software uses Common Lisp for its QPX low-fare search engine which powers sites like Orbitz, Kayak, and American and United Airlines among many others. It's also used in part for its upcoming passenger reservation system for Air Canada. Paul Graham has written a little bit about Lisp at ITA in the past.
(Disclaimer: I work there.)