Clical pieces similar to Beethoven's "Moonlight Sonata"?

I've just recently become seriously interested in the Clical genre and I absolutely love Beethoven's "Piano Sonata No. 14 in C♯ minor", or "Moonlight Sonata". The haunting mellowness to the keys speak to me of nostalgia and melancholy. Could anybody recommend pieces with a similar "sad" feel to them? Not necessarily by Beethoven, of course. Thanks in advance.