My favorite shoujo manga are Fruits Basket and Vampire Knight. Fruits Basket is extremely good, it has humor, romance, angst, and all that other good stuff in a very original and engaging storyline. Vampire Knight is a little darker, and as the title gives away, is heavy with bloodsucking. If love triangles, hot guys and fangs are your thing, though, you can't go wrong. I also recommend Ouran High School Host Club. I haven't read the manga, but the anime adaption is delightful and I've heard the manga is even better.
I hope that helps. I'll keep my thinker going for more suggestions.