Custom keywords including tags and category list within (hardcoded in header.php)

gistfile1.phtml

<meta name='keywords' content='<?php echo $keywords; ?>' />
<meta name='description' content='<?php echo $description; ?>' />

header.php

<?php
# Add to top
# Should be in theme options as functions
$keywords = "define, here, your, default, seo, keywords";

if (is_home()) { 
	$description = get_bloginfo('description');
} else if (is_single()) {
	$description =  $post->post_title;
	$tags = wp_get_post_tags($post->ID);

	foreach ($tags as $tag ) {
		$tagslist .= $tag->name . ", ";
	}

	$keywords = $keywords.", ".$tagslist;
} 
else if (is_category()) {
	$description = category_description();
}
?>