• Highly customizable "quick and dirty" utilities for doing everyday things. (i.e. as the most powerful scripting language available).
• Large, complicated, mission critical applications which would be impossible to develop in any other language.
• Fast prototyping and Rapid Application Development (RAD).
• Continuous-availability applications, especially those that require functionality changes after initial deployment.

It is sometimes used to define every aspect of an application, sometimes just the internal processing engine (i.e. the guts, without the User Inteface), or sometimes just the user interface. Sometimes it is used as the "glue" to interactively develop Graphical User Interfaces and sometimes to define graphics/windowing systems themselves.

It is often used to provide interactive command languages, macro or scripting languages, and extension languages embedded within commercial systems.

It is widely used to programatically generate other, static, stand-alone applications, in the same or different language. It is also used to generate "mobile code".

Xanalys, a major commercial Lisp vendor, has placed an excellent paper titled Common Lisp: Myths and Legends on their site. From the introduction:

This year, 1998, Lisp is celebrating its 40th year supporting the world's most complex applications. And Lisp has grown a lot in that time. So if you or someone you know harbors fears or concerns about Lisp because of something learned in a class or muttered by a friend 20 or 30 years ago, it's time to take a fresh look. In this paper we're going to survey what Lisp is today.

This site lists a sampling of commercial uses, listed by industry, and reasearch uses.

This site also gives a description of Lisp and its features, available tools written in Lisp, and a comparison with other languages.