Rainer Joswig posted to reddit about a Flash game called Neuroarena. The forum discussion has some cool screenshots, and later in the discussion the developer Karol outlines the use of SBCL to support the game:

Battle server is written completely in Common Lisp (no C library used). We use SBCL (www.sbcl.org) which proved to be an absolutely fantastic development *and* production tool (we had just one minor hassle with garbage collector conservatism). It is used for all the actual game computation:

keeping correct state of world (collision detection, ...) pathfinding AI

For the AI, we have created our own visual language/compiler for describing AI based on graph representation, and that language is compiled using CL to quite performant native code. We are using library I wrote some time ago for matching graph patterns describing the the AI behaviour (http://common-lisp.net/project/patg)