Some of my favorite classical sonatas:
Mozart:
Variations K. 265 (you've definitely heard of these - they're fun, audience pleasing, and great for technique)
K. 283 (probably grade 7ish)
K. 284 (first movement grade 8, last movement more difficult/long)
K. 332 (outer movements both grade 8)
K. 311 (first movement grade 7/8ish, last movement more difficult but doable)
K. 330 (should be doable)
K. 457 (around the same level as K. 332 - often perceived as harder but I haven't found it to be the case)
Haydn (not quite as familiar with these - I'm more of a Mozart person

):
Hob.XVI.20 in C minor (I prefer Haydn's major key works, but it's still a nice/original sonata)
Hob.XVI.23 in F major (especially this one! Not hard and wonderful)
Hob.XVI.28 in Eb major
Hob.XVI.31 in E major (another favorite - not hard and not played often)
Hob.XVI.32 in B minor
Hob.XVI.35 in C major (I love this one too)
Hob.XVI.36 in C# minor (first movement may be a bit difficult)
Hob.XVI.37 in D major (played a lot, but understandable since it's so much fun!)
Hob.XVI.49 in Eb major (more difficult than the others, but still probably doable)