This is a simple regular expression I wrote to convert the first letter of an article into a drop cap. It will surround the first letter with a span tag containing the class drop-cap. You can then apply any styling you like to the span with CSS. It will skip over any HTML encoded characters or tags at the beginning of the article as well so it always highlights the first letter of the content and not any HTML formatting.

$article['full_text'] = preg_replace('/^([\<\sa-z\d\/\>]*)(([a-z\&\;]+)|([\"\'\w]))/', '$1<span class="drop-cap">$2</span>', $article['full_text']);