The harp is a beautiful instrument that for some strange reason does not have much of a repertoire. Most pieces I have heard played on the harp were arrangements of piano music (Debussy’s Claire de Lune played on the harp is an example).
Here is a concerto written for the harp by the German composer, conductor, and pianist Carl Reinecke (1824-1910). It is quite a robust and joyful piece and the orchestral part supports the harp very well without overpowering it.
This is a recording done by Fabrice Pierre and the Swedish Chamber Orchestra conducted by Patrick Gallois. You can buy the recording on eMusic. Enjoy!