You can play Ravel’s Introduction et Allegro as a harp-and-piano duet, and Alice Giles did a wonderful recording with several interesting pieces on it. The Salzedo Sonata is a masterpiece, and the crowning jewel of that repertoire. It is very difficult, but not impossible, for the harp, anyway. It’s quite rewarding. I’m sure you’ll find more pieces in the catalogs. My program with piano was the Debussy Danses, the Salzedo Sonata, the Ravel, and the Berezowsky Concerto, with a few solos to open with.