is there a plugin to add description to a tag page?

i have been trying to add descriptions to my tags pages, but i had no luck with php. is there a plugin that can add a custom field for each tag or something for me?
i want to add descriptions to some of my tag pages, since they are getting lot of traffic. i would do this manually with the following code:

<?php
echo '    ';
if ( is_tag(coldplay) ) {
 ' &raquo;  '; include(TEMPLATEPATH . '/articles/coldplay.php');
}
echo '
';
?>

but there are about 100 tags, and i would have lots of “elseif”.. getting a long tag.php page!