As you suggest, the most elegant approach is when your CSS overrides are loaded after the CSS injected by the plugins. This is quite easy to achieve – you just need to make sure that your header.php
calls wp_head()
before it references your style sheet:
<head>
<!-- all the usual preamble stuff goes here -->
<?php wp_head(); ?>
<link rel="stylesheet" href="https://wordpress.stackexchange.com/questions/2680/<?php bloginfo("stylesheet_url'); ?>" type="text/css" />
</head>