Beethoven Op. 49
Or Pathetique
Or Moonlight
Mozart's a major sonata, the one with the variations and the turkish march. Check out some of the Schubert impromptus, they're pretty long too. OH Schubert's A minor sonata (no. 16 I think), Schubert's sonata-fantasie in g major. Though these works are not technical monsters, say like the Liszt etudes they're pretty difficult and require a sh*t ton of concentration. I wouldn't call them intermediate but they're definitely doable if you approach them correctly.