SVG is XML-based and it's very easy to output graphics from your code from any programming language. There's a cl-svg library (http://code.google.com/p/cl-svg/) but I haven't tried it. There's also cl-cairo2 (http://www.cliki.net/cl-cairo2) which is based on the cairo library.

For realtime 3d graphics there's cl-opengl (http://common-lisp.net/project/cl-opengl/). I'm using it right now with sbcl and the glut wrapper (cl-glut). It comes with some examples too.