This code uses flash to detect system fonts and then detects via javascript in the browser which fonts will actually 
render.

View a demo at: http://font-detect.s3.amazonaws.com/index.html


<!-- element for SWF to load into -->
<div id="font-detect-swf"></div>

<script src="javascripts/jquery-1.2.6.pack.js"></script>
<script src="javascripts/swfobject.js"></script>
<script src="javascripts/font-detect.js"></script>  
<script>
  $(document).ready(function() {
    
    var fontDetect = newFontDetect("font-detect-swf", "flash/FontList.swf", function(fd) {        
      var fonts = fd.fonts();
        
      // Do something with fonts, which look like: [ { fontName:'Arial', fontStyle:'regular' fontType:'device' }, .... ]

            // for(var i = 0; i < fonts.length; i++) {
      //   var name = fonts[i].fontName;
      // }
    };
    
  });
</script>