One piece that helped me a lot was Brahm's arrangement of the Bach Chaconne for left hand alone. The obvious thing it helped with was just facility with the left hand. But it also helped a lot with freeing up the arm and gaining confidence in making large movements quickly. The left hand has to cover so much territory in rolled chords and arpeggios that it's impossible to do without having a very loose arm and just going for it. Also the rapid chords at the end of the major section helped with the ability to reposition the fingers for an upcoming chord on the fly. All those technical improvements transferred almost automatically to the right hand. And it's a wonderful piece of music.