Two that come to mind off the top of my head
Schubert's Wanderer Fantasie and Liszt's Sonata in b minor - Liszt was fascinated with Schuberts work, and emulated and expanded on the formula used by that piece - a long, single movement work made up by parts that serve as separate movements but nevertheless unified by using the same motif(s).
Mozart sonata in C minor, second movement, and Beethoven Pathetique sonata, second movement. Notwithstanding that both sonatas are in C minor, the beginning of the theme of Pathetiques "Adagio cantabile" is the same as the motif in one of the secondary themes in Mozart's second movement, in the same register, and in pretty much the same character. Coincidence? Hard to believe.