Franz Liszt, he's like Beethoven on crack. Renowned as the greatest technical pianist of the Romantic era. His music is difficult to perform so there are not as many people in the world today that can truly perform his work. His scores were so complex and his style was so passionate that it was said they had to wheel in a second piano during his performances cause he would destroy the piano with his virtuoso

If you must strictly adhere to the Classical era, I suggest Joseph Haydn. His an excellent composer who is constantly overlooked and left in the shadows of Mozart and Beethoven. His style retains the reserve quality of the Baroque period but you can feel the passion that lies beneath his music.