list-fonts.jsx

/**
 * PhotoShop script to list used fonts
 * @author Dave Stewart
 * @date 23 May 2013
 * @url twitter.com/dave_stewart
 */
function listFonts()
{
	// functions
		function checkSet(set)
		{
			for(var j = 0; j < set.layers.length; j++)
			{
				var layer = set.layers[j];
				if(layer.kind == LayerKind.TEXT)
				{
					var font = layer.textItem.font;
					if(fonts[font] == null)
					{
						fonts.push(font);
						fonts[font] = true; // no indexOf() so set a flag
					}
				}
			}
		}
	
	// variables
		var sets = app.activeDocument.layerSets;
		var fonts = [];

	// check layers
		checkSet(app.activeDocument);
		
	// check sets
		for(var i = 0; i < sets.length; i++)
		{
			checkSet(sets[i]);
		}

	// result
		var message = fonts.length 
			? 'The following fonts are being used:\n\n' + fonts.join('\n')
			: 'No fonts used in document';

		$.writeln(message);
		return '\n\n' + message; // check the ExtendScript Toolkit console to copy and paste the list of used fonts
}

listFonts();