Custom HTML markup

Put this in your functions.php:

add_shortcode('my_blockquote', 'my_blockquote');
function my_blockquote($atts, $content) {
    return '<div class="span3 quote well">'.PHP_EOL
        .'<i class="icon-quote-left icon-2x pull-left icon-muted"></i>'.PHP_EOL
        .'<blockquote class="lead">'.$content.'</blockquote>'.PHP_EOL
        .'</div>';
}

Then, on a page/post, just write:

[my_blockquote]Content goes here…[/my_blockquote]

and that’s it.

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// EDIT: To add a quicktag button, put this also in functions.php:

function add_blockquote_quicktag() {
?>
    <script type="text/javascript">
    QTags.addButton( 'my_blockquote', 'B', '[my_blockquote]', '[/my_blockquote]', 'B', 'My blockquote', 1 );
    </script>
<?php
}
add_action( 'admin_print_footer_scripts', 'add_blockquote_quicktag' );