side bar

proper valid html and css – or at least a link to your site ?

apart from some milder validation errors which might not even disturb the design, you have by mistake dumped some php stuff

<?php if (function_exists('get_recent_comments')) { ?>
   <li><h2><?php _e('Recent Comments:'); ?></h2>
   <ul><?php get_recent_comments(); ?></ul>
   </li>
<?php } ?>   

<?php if (function_exists('get_recent_trackbacks')) { ?>
   <li><h2><?php _e('Recent Trackbacks:'); ?></h2>
   <ul><?php get_recent_trackbacks(); ?></ul>
   </li>
<?php } ?>

into your style.css – delete it again and you should be fine.