<?php
function mytheme_admin_bar_render() {
	global $wp_admin_bar;
	// we can remove a menu item, like the COMMENTS link
    // just by knowing the right $id
	$wp_admin_bar->remove_menu('comments');
	// we can add a submenu item too
	$wp_admin_bar->add_menu( array(
        'parent' => 'new-content',
        'id' => 'new_media',
        'title' => __('Media'),
        'href' => admin_url( 'media-new.php')
    ) );
}
// and we hook our function via
add_action( 'wp_before_admin_bar_render', 'mytheme_admin_bar_render' );
?>

Here are some IDs for the default links WP 3.1 adds, found in /wp-includes/admin-bar.php:

my-account / my-account-with-avatar : the first link, to your account. Note that the ID here changes depending on if you have Avatars enabled or not.
my-blogs : the 'My Sites' menu if the user has more than one site
get-shortlink : provides a Shortlink to that page
edit : link to Edit [content-type]
new-content : the 'Add New' dropdown
comments : the 'Comments' dropdown
appearance : the 'Appearance' dropdown
updates : the 'Updates' dropdown

Add/Remove WP Admin Bar Links

wordpress

PHP