A small class to help building the FrontEnd CSS from the WP Customizer Options. Better Readability. Lean CSS. No more PHP Noodles in your styles!

wp_customizer_frontend_css.php

<?php

/**
 * This small PHP class provides you some functions to build the frontend CSS from the WP Customizer Options.  
 * 
 * == Fight the PHP Noodles in your CSS! == 
 * As the resulting dynamic CSS of themes can look ugly, 
 * we thought about a sweet and short solution for this.  
 * 
 * == Better Readabilty == 
 * No need of writing CSS with all that PHP checks and echos inside.. brr..
 * Actually you simply write down which CSS selectors should be defined with what option. 
 * The rest just happens automagically.  
 *
 * == Lean CSS ==  
 * You will only get a CSS style back if a value has been saved in the WP Customizer
 * You can still add static CSS that should be added anyway, no matter if the option has been set
 * You can generate one style from multiple options (for example font size, weight and color just for the h1)
 * 
 * @author Sven Lehnert, Konrad Sroka
 * @license GPL http://www.gnu.org/licenses/gpl.html
 * @package WP Customizer Frontend CSS
 * @since 1.0
 * 
 */
class Customizer_Frontend_CSS {
  
	var $css_tmp = '';
	/**
	 * PHP 4 constructor
	 *
	 * @package WP Customizer Frontend CSS
 	 * @since 1.0
	 */
	function CC_Customizer() {
		$this->__construct();
	}

	/**
	 * PHP 5 constructor
	 *
	 * @package WP Customizer Frontend CSS
 	 * @since 1.0
	 */	
	function __construct() {
		
	}
	
	/**
	 * Add a style to the Customizer_Frontend_CSS object!
	 *
	 * @package WP Customizer Frontend CSS
 	 * @since 1.0
	 */	
	function add_style( $selector, $args = Array() ) {
	
	$this->css_tmp .= $selector.' { ';
	
	foreach ($args as $key => $css) {
		
		$option_value = '';
		
		if( isset( $css['option'] ) )
			$option_value = get_theme_mod( $css['option'] );

		if( isset( $css['value'] ) && !empty($option_value) ) :
			$this->css_tmp .= $css['style'].': ';
			$this->css_tmp .= str_replace("$", $option_value, $css['value']);
			$this->css_tmp .= '; ';
			
			elseif(!empty($option_value)) :
				$this->css_tmp .= $css['style'].': ';
				$this->css_tmp .= $option_value;
				$this->css_tmp .= '; ';
			
		endif;
		
		if(isset($css['static']))
			$this->css_tmp .= $css['static'];
		
	}
	$this->css_tmp .= ' } ';
	
	}
	
	/**
	 * Output the Customizer CSS!
	 *
	 * @package cc2
	 * @since 2.0
	 */		
	function output_css(){
		echo $this->css_tmp;
	}
}

?>

Some Examples how to use this class can be found here:
https://gist.github.com/konradsroka/6326016