Ouran was amazingly funny & I was so sad when it ended. Of all the "girls pretending to be boys" manga out there, this ranks right up there will HanaKimi as one of my all-time favourites.
and now I have the theme song stuck in my head!! I LOVE LOVE LOVE this anime. It's one of the first "newer" anime that I have spent time watching and I can't recommend it enough. Naomi did a GREAT writeup on the series. Make sure you catch it on Funimation.com as well!