Another great Beethoven sonata is the Appassionata sonata, Op. 57. Also, for his slight sense of humor, check out the third movement of his pastoral sonata. You want scary, but still classical? Check out Sonata no. 7's (op. 10 number three) slow movement. It is in D minor, and by today's standards it's not scary, but it is one of the first times that Beethoven brings dramaticism to its height for 1797.
Also, check out Mozart's Piano Concerto no. 24. He wrote that piano concerto in just three weeks! It is amazing, and it actually sounds like Beethoven without the accents that Beethoven would be known for.