Hm.... My favorite romance one would have to be either Peach Girl or Fushigi Yuugi. Other good ones are His and Her Circumstances, High School Rumble (if you don't mind a plotless, comical love story), and Ayashi No Ceres......though the manga is much better than the anime for Ceres. Still remains my favorite manga of all time. Mars is also a good romance manga if you wanted to get into reading as well as watching anime.