As Deacon Lance said,
Saint Romanos is a good choice, especially since many of his Kontakia are still used today (like on Christmas). Other hymnographer saints include
Saint John of Damascus, a monk, iconographer, priest and author of the Paschal Canon;
Saint Ephrem the Syrian, a monk and deacon who wrote many hymns for the Syriac Church; and
Saint Kassiani, a nun who wrote a famous troparion sung during the Matins of Holy and Great Wednesday.
And let's not forget the Prophet and King David!
I believe there's an icon somewhere of the "Synaxis of the Holy Hymnographers" that includes all these saints and more--perhaps someone would know where to find it.
Dave
